Treating Fish That Have Contracted Ick (AKA Whtespot)

by Shelli Wittig (Fishgal)

Photo of fish with white spot

This is a common parasite which most aquarists eventually encounter. Even if you follow quarantine procedures you may at some point acquire an infected fish, which should be treated before being introduced into your main aquarium. The good news is that if handled correctly, this disease can be easily and permanently eliminated.

What Is It?:

Ich has three life stages, which are important to understand for proper diagnosis and treatment.

1 When the parasite is visible to the naked eye, it is a nearly fully developed trophont which has burrowed under the fish's mucus coating where it is protected from chemicals (medication). It has likely been feeding on the body fluid of the fish for several days and has swelled to many times its original size. At common aquarium temperatures of 75 to 80ºF this feeding stage lasts only a few days, at which point the fully developed cyst drops off the fish as a tomont.

2 The tomont may swim for several hours before settling on and attaching to the substrate, a plant, or some other surface. During that time it is susceptible to chemicals and medication will be effective. Once attached, it begins its reproductive stage. It encysts and begins rapidly dividing. At this point, it is again immune to chemicals. Within a few days, hundreds of new organisms burst from the cyst, sprout cilia and start swimming in search of a host.

3 These are now referred to as thermonts or swarmers, and they must find a host within a few days or they will die. (For this reason, we know that even an aquarium heavily infested with Ich would be clean and safe for new fish after only a week or two without fish in the tank.) Medication is effective at this stage. Once the thermont attaches to a host and burrows in, it is referred to as a trophont and the cycle begins again. Unfortunately, with each cycle, the number of organisms in the tank increases dramatically.

Left untreated, Ich is almost certainly fatal. Infected fish are weakened by the ever growing number of parasites feeding on them. Secondary bacteria and fungi attack more easily. Trophonts on the gills eventually restrict oxygen flow and respiration is hindered. The ailing fish will ultimately succumb either to the infestation itself or a secondary condition.

How Do I Prevent It?:

I came into the research phase of this article with certain misconceptions about this parasite. It is a commonly held belief that the Ichthyophthirius organism is always present in your aquarium and needs only the right opportunity, such as stress resulting in a weakened immune function, to attack your fish. Surprisingly, I found no scientific data to support that claim. Credible sources state that there is no long-term dormant stage this parasite can exist in. While its lifecycle is longer at low temperatures (like that of an outdoor pond in a cooler climate), at average home aquarium temperatures this parasite would likely complete a lifecycle in less than a week. Considering that a single organism produces hundreds (if not thousands) of offspring, the logical question is “where would they all go? Dr. Peter Burgess, writing for Practical Fishkeeping magazine (who also co-authored the book entitled A to Z of Tropical Fish Diseases and Health Problems), refers to the dormant concept as rubbish.

The proliferation of this myth could be due to the fact that it is possible for a strong, healthy fish to resist severe infestations, especially if it was infected previously and developed some resistance. While the organisms attach easily to the gills of most fish (where they cannot be seen), the body may be sufficiently protected by a tougher mucus coating. Such a fish could serve as an asymptomatic carrier; potentially hosting many lifecycles without showing any visible signs. When introduced to a new tank it brings the parasite with it. Scaleless fish such as loaches and catfish often show symptoms first, but most likely every fish in the tank will eventually be infected; if not visibly on the body, on the gills at the very least.

It stands to reason that a stressed fish with a weakened immune function is an easy host, but only if the parasite is present in the tank, to begin with. That brings us back to how to prevent it, now that we know it is not lurking in every aquarium waiting to strike. Here are few guidelines:

  1. Never buy fish from a tank where any fish show signs of disease.
  2. Quarantine new fish for 14-21 days and observe for any signs of illness. Do not take low dosage preventative measures against quarantined fish (such as half the recommended medication dosage) as this would only spare the organisms most resistant to medication. If you're going to treat, do a full treatment just as you would if you were certain the fish was infected.
  3. If you do not quarantine (not everyone has an extra tank set up), after floating the bag and adding small amounts of your tank water to acclimate the new fish, gently empty the bag into a net (working over a bucket) and then place the netted fish in the aquarium. Never add the water from the travel bag to your aquarium as it could contain Ich thermonts or other dangerous organisms. Still, your fish could have trophonts on the gills or on the body which have not swelled enough yet to be visible. You're gambling with the health of all your fish if you don't quarantine.
  4. If you keep multiple tanks, use separate nets for each tank and/or let your net dry completely between uses. Ich cannot survive being dried out.
  5. Buy plants only from tanks without fish, or quarantine plants for 5-7 days without fish, or bathe plants in potassium permanganate before putting them in the main tank (unfortunately this can be hard on the plants).
  6. If your tank does become infected, be accurate and thorough with treatment to ensure total eradication. It only takes a single surviving trophont to reproduce and start the whole ugly process again.

How Do I Treat It?:

There are many over-the-counter medications for ich. They all boil down to a few common ingredients, each of which has a downside. In addition, Ich outbreaks often accompany cycling problems and it is difficult to keep up with frequent small water changes (to minimize ammonia and nitrite levels) while dosing with a medication that advises not to do any water changes during treatment. With that said, I'll start by recommending my first two choices for treatment, which are more natural (or at least less chemical) and should be easier on your fish, your biological filter, and your wallet.

Raised Temperature:

There are two schools of thought regarding raising the temperature of the water to treat ich.

  1. The first approach is used simply to speed up the lifecycle of the parasite, since whatever medication you choose will only be effective on the free-swimming tomonts and thermonts. It is understood that at temps above 75ºF, for example, an entire lifecycle can be complete in less than 4 days. (In contrast, it can take more than 5 weeks at temps below 45ºF, such as you might find in an outdoor pond.) Slowly raising the temperature a few degrees above normal (to approximately 80 - 82ºF) will do the trick, and you can treat accordingly with salt or a medication (see below). Always maintain good surface agitation, especially with a higher temperature.
  2. The second approach is to actually destroy the organism with heat, and can be combined with the salt treatment below, but not with meds. The data I studied (including a report by the Southern Regional Aquaculture Center, which is currently archived here) suggests that most strains of Ich cannot reproduce at temperatures above 85ºF. To use this treatment approach, slowly (no more than 1 or 2 degrees per hour) raise the temperature to 86ºF, while maintaining strong continuous surface agitation to oxygenate the water. This is extremely important because water holds less O2 at higher temperatures. (This is why meds should not be used in conjunction with high temp most Ich treatment products also reduce oxygen levels. Less available oxygen, combined with the respiration difficulties an infected fish is already faced with, could be fatal.) You can angle powerheads up toward the surface, or lower your water level to get a little extra splash from your filter return. As with any treatment, observe your fish closely for signs of stress (labored breathing, erratic behavior) and reduce the temperature slowly if necessary. (A note to the wary; my Malawi haps and clown loaches endured a temperature of 88ºF for 10 days with apparent ease I never detected the slightest hint of distress and the Ich was completely wiped out. One article that I read suggests the temperature be raised to 90ºF!)

The adjusted temperature should be maintained for approximately 10 days, or a minimum of 3 days after all signs of the parasite have disappeared. Do not discontinue treatment when the spots go away. This is critical, because we know that they are visible only as a trophont on the body of the host, and not during the reproductive or free-swimming stage. We also know that trophonts on the gills are impossible to see.

One last note on raised temperature treatment: If you follow the directions here thoroughly and have a subsequent outbreak without having added new fish or plants, you may need to try a different approach. It is possible to encounter a resistant strain of ichthyophthiriasis, as there have been rare instances recorded where the organism survived at 92ºF!


Salt is frequently recommended for treating a myriad of fish diseases, especially those involving external protozoa and fungi.

What kind of salt? We are not talking about marine salt or cichlid salt (both of which typically contain a blend of mineral salts and trace elements specially formulated for aquarium use to simulate ocean or rift lake water chemistry). You want sodium chloride (NaCl). Aquarium salt is the most widely used form because it does not contain the iodine or anti-caking agents that table salt does. I will say, however, that several credible sources assert that the minute amount of additives in table salt are harmless. Robert T. Ricketts, writing for AquaSource online magazine, puts it best with any water-living vertebrate would be pickled in brine well before toxic concentrations of iodine could be reached. Still, others offer strong warnings about the dangers of iodine and prussiate of soda (an anti-caking agent) and suggest canning salt as a cheaper alternative to aquarium salt. Make your own choice, but since I've heard only warnings and no actual accounts of fish death by table salt, I assume it's most likely the better safe than sorry principle at work here. Sea salt is another option, and is generally available in nutrition stores because it is considered a more natural form of salt. It does not contain iodine, but may have anti-caking agents. I have used it in my aquariums without incident.

Can my fish handle salt? I wrote this article with African rift lake cichlids in mind, and I have successfully exposed my Malawi haps and clown loaches to a salt treatment without any problems. But these fish are accustomed to fairly hard water with a high pH. It is my understanding that species preferring soft water will not tolerate salt as well. If you keep soft water fish, please do your homework before proceeding with salt.

How much? I visited websites and read articles on treating Ich in generic freshwater fish, food fish, guppies, loaches, and African rift lake cichlids to name a few. I encountered dosage recommendations ranging from about 1.75 tablespoons to 6 tablespoons salt per 5 gallons of water. One rift lake cichlid importer/breeder uses 1 handful of salt per 5 gallons of water. I concluded that my fish can probably tolerate more salt than I think, at least on a short-term basis. Based on everything that I've read to date, I would feel comfortable adding 2-3 tablespoons salt per 5 gallons if I were also using the high temperature treatment outlined above. If I were using salt alone, I would work my way up to 4-5 tablespoons per 5 gallons. We don't want to skimp on our treatment if we hope to permanently eliminate this pest. Salt should be added slowly over the course of 24-48 hours or so (always dissolve in a small container of tank water first). Keep a close eye on your fish and perform an immediate water change if they show any additional signs of stress (beyond what the Ich is already causing).

How long? The salt bath should be maintained for approximately 10 days, or for at least 3 days after any visible signs of Ich can be detected. Do not discontinue treatment when the spots go away. If you use a higher dosage of salt, watch the duration more closely. One article (on guppies) specifically stated not to leave the fish in salt longer than ten days, but their dosage recommendation was on the high end at 5 tablespoons per 5 gallons.

What else should I do? The salt bath can be used on its own, or in conjunction with a temperature adjustment as described in the section above. A water change can be performed during the salt treatment (but is not necessary unless nitrates are creeping up to an undesirable level). Be sure to salt the replacement water accordingly to maintain salinity. Gravel vacuuming is also helpful to remove as many tomonts as possible before they can release offspring. Again, this is not absolutely necessary since the salt should destroy the free-swimming thermonts upon their release.

At the end of the treatment, do several large (40-50%) water changes with dechlorinated unsalted water to reduce the salinity to normal.

One last note on salt treatments: If you follow the directions here thoroughly and have a subsequent outbreak without having added new fish or plants, you may need to try a different approach. It is possible to encounter a resistant strain of ichthyophthiriasis, as there have been rare instances recorded where the organism survived in water salted at more than 5 tablespoons per 5 gallons.

Traditional Medications:

As stated previously, there are many products available for treating ich. Whatever you choose, be sure to:

  • Read the label thoroughly for dosage information, special instructions, and warnings related to your own health and that of your plants, invertebrates, and scaleless or sensitive species of fish.
  • Perform a water change and vacuum the gravel before medicating. Most meds are less effective with excessive dissolved organics (nitrates) present and you're often instructed not to change any water during treatment.
  • Remove the carbon from your filter.
  • Maintain good surface agitation and water movement. This is always important, but it is absolutely critical when raising your water temperature and administering meds both of which reduce the oxygen content of the water and can kill your fish if care is not taken. For that reason, it is not advisable to raise the temperature more than 2 degrees above normal when using any of the following Ich treatment products.
  • Continue treatment for the duration advised. Because of the lifecycle of the parasite, it is critical that you continue treatment for a minimum of 3 days after any visible signs of Ich can be detected. Do not discontinue treatment when the spots go away. If the instructions advise you to retreat, do so.
  • Disregard grandiose claims. Some products claim to cure ick within 24 hours. Based on what we know about the lifecycle of this parasite, that is simply not possible.

Copper-based medications are commonly recommended for treating ich. Some brand names include CopperSafe® by Mardel, General Cure® by Aquarium Pharmaceuticals, and Aquari-Sol®. Look for the active ingredient copper sulfate or soluble copper salts. Copper does not stain and is highly recommended by some aquarists. It does have drawbacks, however. It causes oxygen concentration to drop, it is toxic to snails and invertebrates, it may not be tolerated well by scaleless fish and plants, and like any chemical, it can certainly be toxic to your fish especially if dosed incorrectly. Apparently, the toxicity increases as total alkalinity (KH) decreases. This would suggest that copper-based meds may be better suited for use with African rift lake cichlids than with soft water fish from low pH/KH conditions. But beware; if you should have a drop in your pH while using copper your fish could perish.

Potassium Permanganate has been suggested as an alternative to copper for treating ich, especially in soft water fish. It is primarily used in ponds, and is not, in my opinion, the best choice for aquarium use. It most certainly is not for the beginner. It can be purchased under its chemical name or found as the active ingredient in products such as Flukes Control® by Aquatronics. As with so many chemicals, there’s a fine line between calling it a wonder drug and a lethal substance. It is not really a medication but an oxidizing agent that reacts with organic material, resulting in the destruction of external bacteria, fungus, and parasites. For that reason, it is considerably less effective with excessive nitrates present, because its oxidizing power is “used up” on the dissolved organics in the water and is consequently not effective against the target pathogen. It is often used by retailers as a dip for incoming plants, to eliminate snails and their eggs. It is toxic in high doses, especially in high pH water; there are better choices for treating African rift lake cichlids. It is not safe for eggs and fry, and excessive treatments can cause gill damage in adults. It will damage your biological filter, kill algae, and reduce the oxygen concentration in the water; strong aeration and water movement is critical. It can be tough on live plants and catfish, and should not be combined with any other chemicals – especially Formalin. It can burn your skin and eyes, and will stain your hands and clothing brown; gloves are recommended. It cannot be removed with carbon like other meds; it is neutralized with hydrogen peroxide but I don't know exactly how that is accomplished safely in the aquarium. Again… this is for the advanced fishkeeper.

Formalin is a form of formaldehyde and is often used by fish farmers and home aquarists to treat ich. It can be purchased under its chemical name or found as the active ingredient in products such as Ick Guard II® by Jungle, and Formalite III® by Aquatronics (which also contains copper). While it is non-staining and said to be safe for live plants (and at lower dosages…) scaleless fish, eggs, and fry, it is nevertheless a strong chemical a preservative for biological specimens (AKA embalming fluid). It may damage your biological filter, deplete oxygen levels in the aquarium, and destroy invertebrates and weak fish. Its toxicity increases with water temperature and acidity, making it a questionable choice for soft water fish.

Malachite Green is an ominous substance that’s highly effective against Ich and fungi. It can be purchased separately under its chemical name, or found as the active ingredient in products such as Maracide® by Mardel, Ich Cure® by Aquatrol, Super Ich Plus® by Aquatronics, and Fungus Plus® by Aquatronics. It is carcinogenic and dangerous to handle or breathe (especially for pregnant women). There are rumors circulating that it could be banned for aquarium use by the FDA in the future. It cannot be used on food fish and is toxic to eggs, fry, some varieties of tetras, catfish, elephant noses, loaches and small marine fish. It also may damage your biological filter and will likely stain aquarium decorations and silicone sealant. Malachite Green is light sensitive, and you will be advised to keep your aquarium lights off during treatment to prevent the chemical from oxidizing.

Formalin and Malachite Green are often used in conjunction with one another. The two chemicals are said to have a synergistic effect when combined, having a greater impact together than either one by itself. Products include Rid-Ich+® by Kordon, Quick Cure® by Aquarium Products, Cure-Ick® by Aquarium Products, Ick Guard® by Jungle, and Formalite I® by Aquatronics. This combination of chemicals is probably the most common choice for treating ich.

Acriflavine is a chemical found in some Ich medications such as Ick Clear® by Jungle, and Acriflavin Plus® by Aquatronics. It is considered to be highly effective against protozoan parasites, as well as external bacterial infections and fungus which sometimes occur as a secondary condition. It may damage your biological filter, harm live plants, cause skin irritation, and stain your hands and tank decorations; gloves are recommended. I do not know how well it is tolerated by invertebrates, sensitive species, scaleless fish and fry, but I do know that it cannot be used on food fish which is sometimes a clue as to the toxicity of the substance. As always, read warning labels thoroughly.

Methylene Blue is used primarily for superficial fungal or bacterial infections, and nitrite or cyanide poisoning. It is also considered to be an alternative to Malachite Green for the treatment of fungus and external protozoa in sensitive fish, eggs, and fry. It is available under its chemical name or in products such as Methyblu® by Aquatronics. It too cannot be used on food fish and is a powerful dye that may stain tank decorations and silicone sealant. Damage to plants and biological filter may also occur.

There are other antiparasitic medications available, but I believe I've covered those most commonly used. Clout® by Aquarium Products is one more worth mentioning since it appears on nearly every LFS and pet store shelf that carries fish and is often recommended as a cure-all. It is an extremely strong blend of medications which I am unfamiliar with, including dimethylamino, phenyl benzylidene, and cyclohexadiene. I believe it is best suited for internal parasites. It is definitely not to be used with scaleless fish. Read the label carefully.

Alternative Medications:

There are a few products that have been developed which take a completely different approach to treating Ich than those outlined above. One is Stop Parasites® by Chem-Marin. It utilizes a proprietary blend of food-based ingredients including hot peppers, which may be safer for you and your fish than traditional meds. According to its creator, the product took eight years to develop. It apparently stimulates the fish's slime coat production to excess, which causes the parasites to slough off, or be shed. Then it provides a false host for the parasites to feed upon which is more desirable than the fish. Kent Marine makes a similar product for saltwater parasites called RxP®. I cannot endorse either product, never having used them, but if you are open to homeopathic-type treatments and want to experiment with something other than salt or raised temperature, this product might be for you.

A Final Word:

Most strains of Ich will respond to the treatments described here. However, researchers have recorded rare instances where trophonts were able to encyst and reproduce without leaving the body of the host fish, essentially skipping the second life stage described above. Obviously, this is a menacing thought, but one to be considered should all attempts to eradicate the parasite fail. In such an event, it would be impossible to destroy all the organisms and the frustrated hobbyist would fight an endless battle with repeated outbreaks of the disease. Euthanasia would be the only humane option. Let me stress, however, that I read about this in a research paper and have never heard of this actually occurring to a fellow aquarist. Let's hope it never does.

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