Understanding and Treating Ich (Ick, White Spot Disease, ichthyophthirius multifiliis) in Goldfish and Other Aquarium Fish

by Adam Till

A Note Of Warning About Goldfish Disease and The World "Wild" Web

First off, I'm very sorry that you're having trouble with your goldfish.

There is an awful lot of conflicting information on the web, and most if it is because of websites repeating information from other websites without having direct experience with treating disease themselves. Usually this is best recognized by the lack of original photographs of the disease processes, and a lack of references to claims made in the article or treatments suggested.

Please be careful treating your fish using such information, and always contact an aquatic veterinarian for assistance whenever possible.

Since I am just a breeder and not a vet I cannot legally diagnose or prescribe a course of treatment for your fish, so instead I will simply offer a description of what I do when I encounter these issues.

Short Take

Let our little goldfish paste give you a quick intro...

As one of the most common (and thankfully most treatable) parasite-caused diseases in goldfish, ich generally shows up as a collection of large white dots on your fish.

Although there are a host of natural treatments involving heat and salt, some take too long to be effective for really sick fish, place even more stress on them, and can cost as much in aquarium salt as the most effective medicines.

Although we'll talk about all of these methods and more, if you're just looking for the quickest and easiest method for your fish, I use Ich-X by Aquarium Solutions/Hikari.

When I treat ich I raise my tank temperature to 75°F with a heater and use 5 doses of this very inexpensive medicine (once per day).

In a few days usually my problem is gone, and with none of the fuss, stress, and uncertainty of the heat-based methods.

Ich-X By Aquarium Solutions
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Here's a video of a sad little goldfish with ich taken at a local store. You can see the characteristic white spots, clamped fins, and overall sick demeanor that comes along with ich.

How Can I Tell If My Goldfish Has Ich?

Ich is one of the most common and easily recognizable protozoan diseases that affects goldfish and other aquarium fish.

In fact, it's actually one of the few that doesn't generally require a microscope to positively identify. A simple light microscope can be used in combination with a skin scrape to get a positive ID if you happen to have those available. Although there are some other diseases that have a similar appearance, they don't tend to affect the sort of fish you're likely to keep.

Disease Signs and Symptoms for Ich

Early signs (warning signs):

  • irritation, shown by flashing (scratching) against rocks and gravel
  • loss of appetite or reluctance to feed
  • decreased activity level, less swimming and exploring

Advanced signs (fish is already very sick):

  • small white spots resembling sand
  • pale coloration of gills, swollen gills (should normally be pink and healthy)

Most of the time people will only actually realize that their fish are sick when the characteristic ich white spots finally appear.  If you're observant and know your fish well you'll pick up on the earlier symptoms before that point.

Flashing Against Rocks and Gravel

Since fish lack the ability to scratch themselves any other way, when they're itchy you'll often see them brushing themselves against the bottom of the tank or against rocks and decorations.

Seeing this briefly once in a while is quite normal. If the fish is doing this repeatedly, especially to the point where they look uncomfortable, this is a warning sign that something is bothering them.

A lot of people will bring out dewormers to treat fish that are flashing (thinking that it's that sort of parasite), but flashing is common for fish affected with ich as well. A lot of dewormers will have no effect on ich.

Loss of Appetite

Most of the fish you keep will just about tear your hand off once they figure out that you're the bringer of food (our big orandas often splash us in the face in excitement). If you are noticing that your fish doesn't come up to be fed it should be considered a big red flag.

New fish that won't eat might just indicate nervousness or that they're still getting used to their tank and surroundings. A fish that previously ate well but one day stops is a bad sign.

Decreased Activity Level

Again, given that most fish you keep will tend to be really active for much of the day, one that's suddenly taken to sitting on the bottom, floating around listlessly, or just swimming a lot slower than normal should be watched carefully.

Small White Spots All Over The Body

The usual description that most people give for a goldfish that has ich is that the fish looks like it's been dusted with sugar or salt crystals. That's a generally good description,with a few qualifications.

  1. if the dusting is only on a very specific part of the outside of the fish, it's probably not ich. Dots in the fins only, for example, are usually benign cysts or something of the like. Ich noticable on the body of the fish will usually be spread all over rather than just on one portion.
  2. if the dots are extremely tiny and look more like powdered icing sugar than grains of sand or table sugar crystals, you might be dealing with velvet rather than ich.
  3. some white dots on goldfish are not ich. Goldfish are known to develop breeding tubercles when in spawning condition, and white spots on the wen (head bouquet) of a goldfish are normally a sign of healthy wen growth. Neither are ich.

Not all white spots on goldfish are ich! This shows breeding tubercles on a male goldfish.

These ich "cysts" are caused by the adult ich parasite digging a hole in the fish and creating a lesion from which to feed on it. If that sounds painful for the animal, you can rest assured that it certainly is. This is why infected fish often flash against rocks to try to get rid of what's causing the pain or irritation.

One of the downsides of pale or white fish is that these cysts may be tricky to spot, so take an extra careful look at any white fish that starts to show one of the earlier symptoms listed above.

In any case, by the time these dots are visible on your fish, be aware that it's already extremely sick. Trying one of the more stressful "natural" treatments that seem so popular at this point can be why the fish ends up dying. It may seem cheaper or easier to just raise the temperature of your tank and/or to add some salt, but that may stress your fish. Your fish can't handle that stress if it's already quite sick.

Showing white spots

Pale Coloration Of And Swollen Gills

If the white ich spots are only present in the gills of your fish, you may never see any body spots at all before the fish ends up dying.

For this reason, it's a good idea to handle your healthy fish gently once in a while to take a peek into their gill area. If you get a mental picture over time of what healthy gill tissue looks like and you one day notice the fish flashing, not eating, or getting lazy, taking a look at their gills to see if they're dull or swollen may give you warning someone else would miss.

Since handling a fish can be quite stressful on it, consider picking up some API Stress Coat for use when you do so.

By rubbing some Stress Coat on your hands before handling the fish (wear gloves if you prefer), you're less likely to damage the slime coat on the fish. The aloe vera in the product is actually included to help promote a healthy slime coat, so you're really using the product in a unique and useful way by doing this.

API Stress Coat Plus
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Consider doing your fish inspection during water change time once in a while, for a couple of reasons. The fish will be easier to catch, and if you decide to add Stress Coat to the water as well be aware that it does have a dechlorinator built in. To ensure you don't accidentally overdose that part, just replace your usual dechlorinator (like Seachem Prime etc) with this product for that water change.   

Why Did My Fish Get Ich?

In a nutshell, your fish got ich because it was in the water with them and they weren't healthy enough overall to fight it off. Let's unpack that a little further.

First off, although the prevailing wisdom in the fish hobby is that ich is present in all tanks and healthy fish just don't become sick from it, that's not quite true. Contrary to popular belief, ich isn't actually even present in well-maintained aquariums or ponds.

The reason it's not found in those tanks is because some people take the time to quarantine their fish before adding them to a community tank and treat for ich in quarantine (Ich-X is one of our quarantine medications here). Quarantine involves keeping any new arrivals in a separate tank for a month or more before introducing them to the main tank, and is an important choice for protecting the health of any animals you may already own.

If all ich parasites are killed in quarantine and care is taken not to introduce contaminated water from later fish, plants, shrimp or snails, then fish literally can't get sick from ich because it isn't even around.

In some tanks where ich is present but the fish aren't showing symptoms, that's usually because the ich parasites aren't present in large enough numbers to cause a problem. If the fish don't have health or stress problems which cause them to break out with an active case of the disease, the tank may appear to be "ich free" despite fish there having a low grade exposure to them. If a few water changes or late or the fish become stressed, however, the infection may bloom to dangerous levels quite quickly.

As a result, if your fish is showing ich symptoms, it's because the fish itself isn't strong enough to fight the disease off, or the tank is making that impossible.

Feeding good foods, keeping small numbers of fish in large tanks, and lowering stress levels for the fish can all help prevent this in the future (more on that subject later).

How Can I Get Rid Of Ich Quickly?

Before starting any chemical treatment, be sure to remove all carbon from your tanks. Carbon will remove any medication from the water. Please note that a lot of filter cartridges contain carbon, and therefore the cartridges may need to be cut open to remove the carbon (while leaving the floss that contains your actual filter bacteria).

Next, realize that moving infected fish from a display tank to a hospital tank is completely pointless unless ALL fish are moved, since the ich parasite will survive for a number of days or weeks even without fish present. There's no point in getting a fish healthy in a hospital tank only to place it back in an infected display tank.

In my world, treating ich (only ever found in quarantine tanks) is a matter of a few doses of Aquarium Solutions Ich-X:

Ich-X By Aquarium Solutions
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Unfortunately, even with Ich-X, ich isn't a disease that lends itself to being defeated quickly. This is because the ich parasite is almost impossible to attack when it's in the cyst stage (the white dots).

Label side of Aquarium Solutions IchX Bottle

Medications or heat can only affect the parasites that are in the water and swimming around, not ones that are in the little white spots. You need to wait for each generation to hatch and start swimming, and have treatments in place for when that happens.

If you only treat once or for a short period, you may knock out one generation of ich. Wait a short period for the next generation to come along, however, and you're almost back to square one. This is why it can seem like a frustrating disease to deal with for newcomers, who generally stop treating when the first round of white spots goes away.

Knowing this you'll see how ich isn't a "once and done" sort of exercise, and the next section on heat will tell you how many doses will be required at whatever temperature you keep your tank.

Adjusting the Temperature To Speed Up The Life Cycle of Ich

A lot of talk about temperature and ich is focused around speeding up the lifecyle of the parasite. Life being what it is however, that process is a bit of a double-edged sword. If you plan on using temperature in your battle against ich it's important to understand that there's more to it than just "raising the temperature".

At low temperatures around 60°F like most people seem to want to keep goldfish in some places, ich has a relatively long life cycle (~6 days or so). The ich parasite is healthy at this temperature, so chemical treatments would need to be used tp actually kill it (5 treatment cycles spaced 3-5 days apart being recommended).

At warmer tropical temperatures (75–79°F) close to the temperature most breeders find to be an ideal place to raise goldfish (73°F), ich reproduces and dies off about every 3 to 6 days and should be treated daily (3-5 treatment doses).

At higher temperatures than this, you need to start being very careful with goldfish. With lots of food, strong aeration using air stones and air filters, and a lot of water changes goldfish can last even up to 90°F or a little higher, but this is starting to stress their metabolism and immune systems quite a lot.

That said, it has been found in lab studies that most strains of ich do not infect new fish at 85°F (Johnson, 1976), stop reproducing at 86°F (Dr. Nick St. Erne, DVM), and die at 89.5°F (Meyer, 1984). Just be aware that there are new heat and salt-resistant strains in the hobby in some areas, so these older findings may not apply to your strain.

As well, remember that high temperatures are stressful on the metabolism of even healthy fish due to changes in metabolism and a lack of water oxygen at higher temperatures, so fish already struggling with a disease that affects both their gills and body may not be able to take the added stress from heat.

If you use heat and don't see dramatic improvement within 3-4 days (or the health of your fish seems to decline visibly), stop trying to treat with heat and consider an alternative.

A safe middle ground can be found in raising your temperature to about 75°F with a good heater and doing the 3-5 daily doses of Ich-X. That avoids prolonging the treatment time required at lower temperatures, but avoids the heat stress and added water maintenance required at 86°F and above.

Remember to adjust the temperature of your aquarium slowly over the course of a number of hours. Ideally you'll change your tank temperature no more than a few degrees each hour. If a large adjustment is required between your normal temperature and a "treatment temperature" and you have a very sick fish, this another argument for not relying only on temperature as a treatment method. This is because the fish's metabolism is linked to temperature, and getting that out of sync too quickly can make their problems even worse.

Closeup of starting to show active ich infection

Helpful Adjustments to Your Aquarium To Help Get Rid of Ich

Regardless of the method you choose to actually eliminate the ich parasite, there are a few fishkeeping adjustments you can make in order to have the process go smoother.

None of these are strictly required (so please don't panic if they sound dramatic), but they can make the life of a very sick fish a little easier.

Increase Aeration / Make More Bubbles

Since most methods of treating ich will involve raising the temperature at least a little, this will change the metabolic rates of both the parasite AND your fish. At higher metabolic rates, both the immune response and oxygen demand of your fish increase.

Unfortunately, warmer water carries less oxygen naturally, so you'll do well to increase the aeration in your tank (unless you're already running sponge filters, a bubble wall, or the like).

That can be accomplished by adding a bubbler of some fashion if you don't have one (these plastic air stones are trivially inexpensive when combined with a small air pump):

Never Clog Plastic Air Stone
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Aquatop AP-50 Air Pump
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...or if you have a filter that uses a return of some form you can drop the water level so that the return causes a waterfall and splash effect.

Since oxygen and CO2 levels are basically independent in a tank, there's no real need to disable a CO2 injection system should you have one running.

Betta in QT with ich spots

Here's a betta in quaratine just starting to show ich spots (more obvious ones later on in the article). Can you see the first spots forming?

Do Daily Partial Water Changes

Doing some form of partial water change each day will have a number of benefits for an aquarium fighting an ich infection. These include:

  • helping to bring extra oxygen in to the water if your water source is aerated (ie not from a well)
  • removing hatched and free swimming ich parasites
  • helping to keep water quality up by removing any ammonia, nitrite and nitrate that may be present

The actual amount of the water change can be whatever is most common for your tank during a regular water change. Since filter bacteria are not found in the water itself, there's no danger of causing filter issues from that perspective.

If you're not used to doing large changes don't start now however, or you may cause a largely cosmetic (but scary looking) cloudy water bacteria bloom. If that occurs, you can either ignore it and keep changing water, or stop changing water and the bloom will die away on its own (water changes won't help "fix" bacteria blooms).

Adding Stress Coat at this time will also potentially help speed healing, since the parasites will leave behind small wounds as they break off after reproducing. 

Use a Fine Filter To Remove Parasites

Since the goal of the exercise here is to kill or remove ich parasites at the only time they're vulnerable (when they're free swimming), one slightly unusual option is to capture them with a fine filter.

If you combine the Aquaclear Quick Filter:

Aquaclear Quick Filter Powerhead Attachment
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...with an Aquaclear powerhead (choose the size best suited for your tank, with most not needing more than the smaller sizes):

AquaClear Powerhead 20
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...you can actually quite easily nab the ich parasites when they're swimming. Another option is a diatom filter, but these aren't widely available anymore.

The reason this works is that this style of filter is designed to get micron-sized particles from the water quickly, and ich in its smallest free-swimming stage is 30 microns in size. As a result, they get picked up easily by the micron filter.

If you wash these daily in hot water, you can make a noticeable difference in how many ich parasites you'll encounter on your fish.

This option isn't required, but for those that want to go the distance they're an interesting option. Just be sure your water doesn't have a lot of debris in it to start or you'll clog a fine filter like this very quickly.

Go Bare Bottom

If you can easily remove the substrate/gravel in your tank, or have access to a separate tank, this provides much fewer attachment sites for the ich parasites to lodge.

It's much easier to siphon a bare bottom tank to get rid of the debris that's harboring the parasites after all.

Group of sick ryukins

Alternatives to Ich-X For Killing the Actual Ich Parasite

Commercial Medications

Malachite Green is the active ingredient in Ich-X, and if you read the label of whatever medication you find at your local store and see that, you're probably getting a very similar product.

Hikari says their product contains a less-toxic form of the chemical, and since I've never had issues using it that's what I typically recommend.

That said, here are a few other products that contain similar compounds that I found with a quick comparison search (in theory, they should all get the job done too):

For our UK friends:

Aquarium Salt

Aquarium salt is defined by most people as normal table-type salt that contains no iodine (although the actual harm possible from using iodized salt is of some debate). As a result, the aquarium salt available in stores really has no advantage over any other type of salt other than being in a convenient, normally less expensive volume.

The use of aquarium salt in treating ich infested fish can take many forms. Ideally it's used mainly in plant-free aquariums, however, since many aquarium plants don't handle salt very well.

Salt To Reduce Fish Stress

In its mildest form, a slight increase in salinity (salt level) created by adding 1 teaspoon per gallon of aquarium salt to the tank can help ease the stress on a fish by reducing the work it needs to perform bodily functions (called osmoregulatory stress).

Bulk Aquarium Salt
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Using salt in this fashion can help fish with damage caused by breathing issues or damaged gill and body tissue, but should be stopped when the fish recovers. I personally don't agree with using salt all the time "just in case" because it then becomes less effective when actually needed. Continuous salt in the water also provides a low-level stress on the kidneys of freshwater fish, even if it doesn't directly kill them.

Betta side view showing ich

Salt as a Bath to Kill Free-Swimming Ich

In terms of trying to use salt to damage or inhibit the ich parasite directly, if you keep your tank at a warmer temperature (75°F or higher), adding 3-4 teaspoons of salt per gallon to the tank can help quite a lot. Particularly combined with formalin as described in the next section and used on salt-tolerant species like goldfish, this can be quite effective against most strains of ich (since life isn't fair, some strains of ich are salt tolerant however).

Salt as a Dip To Kill Ich Buried in the Fish

As an even more effective (but substantially more dangerous) option, a strongly-concentrated dip using a separate container is possible. The advantage of this method is supposed to be that the higher concentration of salt will destroy the embedded ich parasites on the fish as well, though I readily confess I have no experience in trying this. 

To perform the dip, first place the fish in a small bowl just large enough to keep the fish covered in water. Place the bowl close to their normal aquarium so you'll able to return them there quickly should things go wrong.

Prepare a separate container big enough to hold at least a gallon of tank water or dechlorinated water of the same temperature. Dissolve 2 tablespoons of salt per gallon of water in that container, swirling it completely until all the salt dissolves.

Pour the salt solution in with the fish very slowly, until it starts to show mild distress (breathing hard, swimming fast etc). This may not require using all of the solution, but try to use as strong of a bath as the fish will tolerate (it should go without saying not to try this with a fish species not known to tolerate salt well).

Leave the fish in the dip for about 30 minutes, but at no time leave the fish unmonitored. If it tries to jump out of the container or loses the ability to stay vertical (rolls over), place it back in the main aquarium right away.

If it tolerates the entire half hour dip, slowly dilute the salt bath with some more fresh water. After doubling the volume of water in the container, return the fish to the display tank (do not pour the salt water into the display tank).

The main tank should still be treated in some fashion to remove ich parasites there, but this treatment is one of the few supposedly able to attack ich on the fish directly.

Should it be required, the dip can be repeated up to three times, spaced at least 48 hours apart.

Aquarium Salt
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Clamped fins and sad ryukin


While not a great option for pond systems due to the cost involved and risks to plant life in the pond, treatment of ich in aquariums using formalin remains a common option.

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Formalin is usually used by dosing 1 ml of formalin per 10 gallons of tank water.

Since extremely weak fish may not be able to tolerate treatment using formalin, if the fish show prolonged signs of stress, perform an immediate series of water changes to flush the chemical from the tank.

A few warnings about formalin use are important at this point.

  1. Handling formalin is dangerous and should be done carefully using proper personal protective equipment (gloves, eye protection and appropriate respirators). Formaldehyde in formalin is a carcinogen and should be respected, and may even form a noxious gas if left unsealed.
  2. Formalin will significantly affect the dissolved oxygen concentration in your aquarium. Using a bubbler system or setting up your filter to waterfall into the tank is critical when using this chemical. Be careful using it around extremely sick fish.
  3. Formalin will kill algae, so never use it on ponds or in aquariums containing green water blooms. The dying algae will cause issues with oxygen and water quality, and will make life even harder for sick fish.
  4. Never use cold formalin solutions (below 40°F) or those that are cloudy or have a white sludge on the bottom of the container. This may indicate the presence of paraformaldehyde (formed under these conditions), which will kill fish very quickly.
  5. Research has shown that formalin at this dose does not have a significant effect on your filter bacteria. Exceeding the recommended dose will impact nitrite-oxidizing bacteria however (the bacteria that convert nitrite to nitrate).
  6. Formalin will cause a potential false positive on hobby ammonia test kits which use Nessler’s reagent (which is most of them). Test ammonia levels prior to dosing formalin for best results. 

For more information on the benefits and risks of using formalin, please read the information contained at this link.

Potassium Permanganate

Potassium permanganate and its strong oxidizing action is a solid option for treating a number of external fish parasites, but isn't a great choice for ich.

Due to the number of treatments required to kill all stages of an ich infection, the cumulative damage to  the skin, gills, and eyes of a sick fish may be more than it can stand.

Generally the recommendation is to use potassium permanganate no more than once a week, and treating ich that would require extremely low tank temperatures to slow down the life cycle of the parasite

So potassium permanganate use is an option, but not a great one.

Betta with ich

Copper Sulfate

Copper sulfate is a very inexpensive option to fight ich and is commonly used in commercial aquaculture operations, but it comes with quite a few drawbacks and caveats.

99% Pure Copper Sulfate Pentahydrate Crystals
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First of all, if you have invertebrates in your tank (shrimp or snails), you're going to want to stay away from any products containing copper. This definitely qualifies, and will kill them quickly.

Second, you should only consider using copper sulfate if you're willing to calculate the exact volume of water in your tank or pond (a "20 gallon" aquarium doesn't actually contain 20 gallons), and to measure the amount of alkalinity in that water. Copper sulfate is extremely toxic in low alkalinity water, and so adjustments to the alkalinity may be required before using it.

If you've never run an alkalinity test before, they work pretty much the same way that your ammonia/nitrite tests do. Just follow the instructions on your test kit, and you'll be fine. These are two options for testing alkalinity:

API KH/GH Test Kit
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Tetra Test Strips 
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To determine the appropriate dosage to use, take the total alkalinity of the tank and divide that number by 100. So:

(Total tank measured at 100 mg/L)  divided by 100 = 1 mg/L dose of copper sulfate

Do not use copper sulfate if your measured alkalinity is less than 50 mg/L. If you aren't willing to test your alkalinity level, do NOT guess and use copper sulfate anyway.

Like formalin, copper sulfate will kill algae as well, so please review the warnings for formalin above (always run heavy oxygenation).

For more information and safety guidelines on using copper sulfate, consult the following link.

Tail fins of a goldfish with ich

How Can I Get Rid Of Ich Without Using Medications/Naturally?

To some degree, a discussion of getting rid of ich naturally comes down to what you consider natural. Is salt natural? What about copper sulfate? Heat? All of those are covered in the sections above.

You'll need to determine what your own beliefs are on that front, and proceed from there.

One thing I will say, however, is that the slower the method you choose to use or the more it stresses the fish, the less likely your fish is to recover from an ich infection. Most people with a bit of experience are a little blase about ich, but it should actually be taken very seriously (especially with new fish which may have internal worms etc as well).

Also keep in mind that medications for fighting ich often end up with a bad reputation only because they're brought in when the fish is already beyond saving.

It's very common to hear about someone trying a heat or salt treatment, getting impatient or not following directions properly, then blaming medications when they're used at the last minute. They tend to be very vocal on internet chat groups when people ask about what to use to treat ich.

In that case it's not actually the medication to blame for killing the fish (since it would have likely have done the job if used earlier), but the delay in applying proper treatment of any sort.

What About Secondary Infections From Ich?

Due to the fact that the ich parasites actually feed off the fish in their active stages, the tiny wounds they create have the possibility of allowing for bacterial or fungal infections to flourish at the damage sites.

As a result, it's a good idea to have some antibiotics and antifungals on hand to treat the fish if required. It's worth noting that Ich-X is also an antifungal, and that's another point in favor of its use.

For bacterial infections, ideally you'd have a microscope available to determine which medicine to use. A gram stain procedure and a book on bacterial infections of fish will both come in handy for those so equipped.

For "gram positive" bacterial infections, erythromycin in the form of API EM Erythromycin is a solid choice (sadly becoming less effective over time, but still part of the Aquarium CoOp "med trio" for a reason). For "gram negative" infections, kanamycin from Seachem Kanaplex is a great option.

Even for those that prefer a natural option, please don't rely on a product like Melafix to solve an active bacterial infection.

Clamped fins are a common sight with any fish with ich

How Do I Make Sure My Fish Never Get Ich Again?

The best way to ensure that your existing fish never get ich is to make sure that you quarantine and treat all fish (and plants, snails, shrimp) that come into your house.

The fish should be quarantined for being hosts of ich, and the others may be shipped in water that contains the parasite. Plants, for example, may possibly come home in water that contains ich simply because lots of stores keep algae eating fish in with their plants. That's not a reason to never buy plants from tanks that contain fish, but doing so merely requires that the plants be kept in a tank without fish at your house for a few weeks before being added.

Since ich is a living organism, it must be introduced into a system in order to cause an active infection. There's a perception in the hobby that ich lies dormant in every fish tank, waiting for a weak fish to infect. That's simply not true, and active management of any aquatic organism coming into your house will make sure you never have to treat your long-term pets.

Although ich is very common in the wild, the reason that it becomes such a problem in home aquariums and ponds is just a matter of relative volume. If a wild fish gets a few ich cysts on it, they eventually burst and release up to thousands of other ich organisms. Though that seems very dangerous, the odds of any of those thousands of ich parasites finding another fish host is actually quite small, so the wild population rarely gets the terrible infections found in our closed environments.

If you lose a fish to ich in quarantine and want to make sure your quarantine tank is clean and ready for a new fish, "cleaning" the tank is simply a matter of heating it to 90 degrees for a week, or leaving it without fish at normal room temp for a month. At that point any ich parasite would have failed to find a host and died off, saving you the need to deal with heavy duty cleaning chemicals like bleach.

Although never having the parasite in your systems is the best defense, if you haven't quarantined up to this point and think you might have some dormant ich cysts in your existing tanks, there are still some things you can do to avoid big problems:

  • keep your stocking density low. Less fish per tank means less chances to spread disease
  • keep up with maintenance so that excess ammonia/nitrite/nitrate doesn't accumulate, pH doesn't fluctuate, oxygen levels don't drop, and other stress causing factors are reduced or eliminated (these will lower the fish’s’ immune response) 
  • clean your equipment with bleach or something similar between tanks, or have separate equipment for each tank if possible. It's very possible to spread both swimming ich parasites and sticky cysts on cleaning equipment and water change hoses
  • use lids to prevent bubblers from transferring ich in water droplets between tanks, or spread your tanks out in different rooms. Need an excuse to have a tank in the living room? This seems like a good one! 
  • proactively treat your tanks with Ich-X or the like to get rid of any low-level infections.

Interestingly, fish that survive an ich infection can sometimes become immune to further attacks.

In fighting off the infection, fish develop antibodies against the parasite. When new ich parasites try to invade the fish, these antibodies attack and isolate the invaders. This not only disables their ability to swim off and infect another host, but causes them to fall off the host fish as well.

This has even opened up the door for vaccines to be developed against ich, which may one day allow prevention of the disease through vaccine rather than chemical (or other) treatment.

Goldfish with clamped fins


Ich is a common protozoan parasite that most aquarium keepers will have to face at some point in their fishkeeping careers.

While relatively easy to dispose of with inexpensive medications like Aquarium Solutions Ich-X or any of the other methods listed in this article, the infection is more than capable decimating an aquarium if not treated promptly and with respect.

The most important part of treating ich is to remember that this is not a "one and done" illness to treat. The characteristic white spots represent a cyst that resists most chemical methods of treatment, and so you must normally wait until they hatch to kill the parasites in the water.

Repeated treatments are necessary, and I personally raise tank temperature to at least 75°F and treat every day for 5 days with Ich-X.

If temperature is used, the following temperature values should also be understood:

  • most strains of ich do not infect new fish at 85°F
  • most strains of ich stop reproducing at 86°F
  • most strains of ich die at 89.5°F 
  • there are some strains of ich that are heat resistant, and will outlast what your fish can deal with

Lastly, ich can only be a long-term problem if not dealt with in quarantine. If ich is killed off by doing a proper isolated quarantine of anything that enters your house prior to it being added to your main display tanks, you'll never have a problem with your other animals.

Good luck!

Aquarium CoOp produced a great video on ich that's well worth watching

Further Reading - What Is Ich Exactly?

Ichthyophthirius multifiliis is a ciliated (covered by small threads that allow it move) protozoan parasite. 

It has a number of different life stages, namely the:

  • trophont stage - where the parasite is on the fish (and is not vulnerable to most chemicals)
  • tomont stage  - where the  parasite is covered by a cyst and is most recognizable (and is not vulnerable to most chemicals)
  • theront stage - where it is immature and free swimming 

Further Reading - Ich Parasite Life Cycle

Once an ich parasite has found a host, its trophont stage invades the area between the thin outer layers of skin or within the vulnerable gill tissue. There, it feeds on the tissues and grows to maturity.

Once it's finished growing, the parasite (now a tomont) leaves the fish and secretes a cyst that allows it to stick to things in its immediate surroundings. There it divides quickly, forming hundreds of immature copies of itself (called tomites).

As the tomites mature, they then become theronts. These theronts escape the cyst by digging their way out, become free-swimming, and start to search for a host.

Theronts must find a fish host in order to complete their entire life cycle.

Remember in all of this, the parasite is only vulnerable to medications in the free-swimming theront phase. All other phases are protected enough to not be easily harmed without risking killing the host fish.

Further Reading - Microscope Diagnosis of Ich

Ich is identified by most hobbyists in the "white spot" stage, but for scientists that does not actually provide an exact ID. This is because ich cysts look very similar to a few less common diseases most people don't usually encounter. Using a microscope to positively ID the parasite itself is therefore required for those who want to be really sure of a diagnosis.

In order to obtain samples, a skin scrape should be performed. Using a glass microscope slide coverslip, scrape lightly down the side of the fish in a head to tail motion to remove some skin cells (ideally, aim for an area contaminated by white spots). This will also bring some mucus with it.

In a vet exam, a small area of fin or gill may be biopsied (clipped), but this should never be done by hobbyists due to the anethestic required for humane gill clips in particular.

In its free-swimming, mature trophont stage, ich is identified by seeing an organism displaying a continual rolling, amoeboid motion. Ich:

  • is visible under 40x magnifiation with a light microscope
  • has a horseshoe-shaped nucleus
  • is oval to round
  • is dark in color,
  • is 0.5 to 1.0 mm in size measured across the widest part of the cell

Theronts (the smaller stage where the parasite is searching for a host) are clear, slightly smaller, pear- or spindle-shaped, and move quickly. They are usually seen continuously spinning on their long axis. Be careful not to confuse them with other organisms like Tetrahymena.

Further Reading - How Does Ich Actually Harm My Goldfish?

Despite being responsible for a huge number of fish deaths in the aquarium hobby, the exact mechanism for how ich damages the fish isn't actually known.

When suffering from an ich infestation, to some degree it will depend on what portions of the fish are most affected.

In the case of an ich gill infection, the gills become extremely inflamed, swollen and deformed (hence why a gill clipping is sometimes performed). This damage harms the fish's ability to extract oxygen to its blood (and hence to be able to breathe), and causes a loss of critical bodily fluids as well.

With a skin infection, ich can cause irritation leading to secondary bacterial and fungal infections. So while the parasite may not kill the host directly, it can weaken its immune system enough that other organisms end up doing this instead.

Adam Till
Adam Till


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