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Using Heat to Treat Ich in Freshwater Tropical Fish

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What is Ich?

Ichthyophthirius multifilis (Ich) is a very common protozoan parasite that finds the aquarium environment a most hospitable location for carrying out its life cycle. Because of the low densities of fish in large volumes of water in the wild, even though every cyst can release hundreds to a thousand or so swarmers, few if any will manage to find a suitable host. Those fish that do get infected will likely have only a single or very few parasites attached to its body, which will soon fall off. The fish will heal and be none the worse for it. In the wild, Ich is really no big deal.

A home aquarium, by contrast, is a confined space packed with many fish (relatively speaking). A single Ich parasite brought in on a new fish can quickly multiply and decimate an entire tank full of fish. Unlike in the wild, every larva has an excellent chance of finding a host, and each fish can end up with hundreds of parasites attached to its gills, fins and body. Such an onslaught is too much, and the fish dies from respiratory distress caused by gill damage, osmoregulatory imbalance caused by the many punctures in the fishs skin, or secondary infections of bacteria or fungi that attack the open wounds.

Ich is also known as White Spot Disease. It is characterized by the presence of small white spots, like a sprinkling of salt, that may appear anywhere on the fish. The fish may dart about in the water, and flick or rub its body against the substrate or other objects in the tank. As the condition advances, the fish may become very slimy, clamp its fins, stop eating, and become very listless.

The standard chemical treatments are often effective, but they can be just as toxic to fish and plants as they are to Ich. Sometimes the medications are not effective. Many aquarists are interested in trying a more natural approach that doesn't subject their fish (or themselves) to potentially dangerous chemicals.

Ich Life Cycle

To better understand how it can be treated, a basic understanding of Ich is helpful:

  •  Parasitic Stage - The first stage (trophozoite) is embedded in the skin of the fish, and feeds on fluids and tissue cells. The fish tries to protect itself by producing more cells around the trophozoite, which leads to the formation of the tiny white spots.
  •  Intermediate Stage - Eventually the trophozoite morphs into a trophont, detaches from the host leaving an open wound, and swims freely until it locates a suitable place to settle.
  •  Reproductive Stage - Once the trophont settles, it forms a sticky wall around itself and becomes a cyst (tomont). Inside, the tomont divides into many hundreds or even thousands of tomites.
  •  Infectious Stage - The tomites are released into the water column and swim freely until they attach to a host, starting the cycle over again. If a tomite doesn't find a host within a short period of time, it will die.
  • The Ich life cycle is temperature dependent. Higher temperatures within its livable range speed up every stage of the life cycle, while the lower temperatures will slow it down. At 18C/64F the cycle takes 10-12 days to complete.

    It has been found that Ich does not infect new fish at 29.4C/85F (Johnson, 1976), stops reproducing at 30C/86F (Dr. Nick St. Erne, DVM, pers. comm.), and dies at 32C/89.5F (Meyer, 1984), [1]


    Now that we know a little more about Ich, we can develop a safe and effective natural treatment plan to eradicate it. A multi-pronged treatment plan offers the most assurance of complete eradication of Ich and TLC for the fishes in your aquarium. As with any treatment, carefully observe the reaction of your fish to any changes you make in their environment. If an adverse reaction occurs, discontinue and try another approach.

  •  Increase temperature to 30C/86F. With tropical fish, an increase in temperature to 30C/86F is usually very well-tolerated. Since this temperature prevents reproduction of Ich, it can theoretically cure the problem by itself. So the first step would be to increase the temperature slowly, 1C/2F per hour until the correct temperature is reached. This temperature should be maintained for 10 days, and then slowly returned to normal. Some fish can tolerate higher temperatures. If your fish are more heat tolerant, try increasing the temperature to 32C/89.5F for the first 3-4 days to kill the Ich. Then reduce temperature slowly to 30C/86F, and hold it there for an additional 6-7 days, or until a total of 10 days have passed. Gauge the heat tolerance of your fish by observing their reaction.
  •  Increase aeration. Increased temperature leads to increased metabolism, which enhances the fishs immune response but also increases oxygen demand. Oxygen is lower in warmer water, so it is very important to increase surface agitation during the treatment to increase oxygenation. In planted tanks with CO2 injection, the CO2 should be turned off and extra aeration should be provided. Carefully observe your fish, watching for signs that they are not getting enough oxygen. If fish are gasping at the surface, you need to provide more aeration. Aeration can be increased by reducing the water level so the filter return makes more of a waterfall and splash, and/or use an airstone placed close to the surface of the water.
  •  Do daily partial water changes. 25% daily partial water changes will provide several benefits: It will keep the water very clean, which will help fish cope with the stress of the disease. It will remove some of the trophonts and tomites. It will add oxygen. This author also recommends the use of NovAqua+ to condition the change water. This product is a dechlorinator and has several additional benefits that help fish under stress, including sealing of the wounds caused by the Ich. If the water changes seem to stress the fish, reduce the size and/or frequency of the water changes.
  •  Use a Micron Filter. The Aqua Clear Quick Filter used with a power head is an easy and inexpensive way to capture both free-swimming stages and the cysts of Ich in water that passes through the filter. A diatom filter can also be used. Both of these filters trap particles as small as one micron in size. The smallest stage of Ich, the free-swimming, swarming tomite, is approximately 30 microns, large enough to be trapped in this type of filter. Change the filter daily with the water changes. The Quick Filter cartridge can be cleaned and reused. Rinse thoroughly in very hot water, or boil for a few minutes to kill any stage of Ich that may be trapped inside. Or use a fresh cartridge. Make sure your fish are comfortable with the current caused by the additional filter.
  • The following optional procedures where appropriate are also beneficial:

  •  Remove Gravel. In a non-planted aquarium and where practical, the temporary removal of the gravel reduces attachment sites for the tomont and makes it easier to siphon the floor of the aquarium where many tomonts will be located.
  •  Use salt. In a non-planted aquarium with tolerant fish, the addition of Aquarium salt at the rate of 1 teaspoon per 4 liters/1 gallon of water disrupts the fluid regulation of Ich. Do not add salt crystals directly to tank. Always dissolve salt in a small amount of tank water before adding to tank. This dosage may be repeated every 12 hours for a total of three treatments. When Ich is gone, salt is removed with daily 25% water changes. [2]
  • A separate salt bath is very effective for individual fishes. The higher concentration of salt will destroy embedded trophozoites on the body of the fish by preventing them from maintaining fluid balance. To prepare a salt bath for small-medium size fish, dissolve 2 Tablespoons Aquarium Salt in 4L/1 Gal. of conditioned tap water that is the same temperature as the tank water. Stir well to make sure all salt is dissolved before using.

    Place affected fish in a container with enough tank water to cover the fish with a little room to spare. A wider container is better than a tall, narrow one, as it allows for better oxygenation of the water, and room for the fish to move about. Add salt solution very gradually until fish just starts to show mild stress. You may not need to add all of the solution. Leave in bath for 30 minutes, carefully observing the fishs reaction to the treatment. Return the fish to fresh water immediately if it rolls over or tries to jump out. Observe the fish carefully during the entire bath period. After the 30 minutes, dilute the salt bath in stages with tank water. Gently net out fish and return it to the main tank. This procedure can be repeated after 48 hours, up to 3 treatments. Do not use salt in planted tanks or with sensitive, soft water fishes. Do not pour bath water into main tank.

    By the end of the 10 days of treatment, all Ich should be gone and the fish will have healed completely from the effects. Keep the temperature up for the full 10 days to ensure that the Ich is gone.

    Most strains of Ich should be eradicated by this heat treatment, but bear in mind that there is at least one strain in Florida that is known to be heat-tolerant [3]. If you do not notice a marked improvement after 3-4 days of this treatment, you should stop and consider another approach.


    It is commonly thought that Ich lies dormant in all fish tanks, just waiting for an opportunity to attack. This is not accurate. However, it is possible that a resistant fish or group of fish can harbor a low level of Ich infection without obvious symptoms until stress of some kind reduces the fish's ability to fight it off. Then the infection becomes full-blown, seemingly out of nowhere. While this is a possibility, the most common and most likely cause of ich in any tank is through the introduction of new fish.

    Ich is present in many fish bred in fish farms and distributed to pet stores. Carefully inspect each new specimen you are considering for purchase. Even fish that appear perfectly healthy can still harbor ich in the gills, or have a new infection that doesn't yet show the typical symptoms. If possible, quarantine all new fish in a separate tank to prevent an infestation of Ich, as well as other potential parasites and diseases. The quarantine period should be two weeks or longer, during which time you should carefully observe the new fish. Anti-parasitic medications or foods can be used during this time to prevent the spread of certain other types of parasites, such as worms and flukes.

    Reader Comments Comentrio

    I wanted to mention brought out discoveries in your article that might be misleading to a reader. In the second paragraph under Treatment it's mentioned that by adding salt it is preventing them from maintaining fluid balance, referring to the ability to perform osmosis. While making it more difficult for a single cell organism to perform such tasks it doesn't make it impossible. A certain gravity of around 1.003 breaks down the cellular structure and the cell implodes. The article also mentions that the protozoan doesn't lay dormant in water. There must be more to this, as neglected tanks causing stress in fish can lead to Ich even after going through a two week 32C quarantine.

    Contributed by Andre' Rowe

    If Ich is present in your aquarium after quarantine, then the quarantine procedure was not performed right. It is absolutely right that keeping an aquarium fish free for a time (preferably 1 month) will erradicate the parasite from the aquarium, but the fish in quarantine could still be harboring parasites in the gills. It is important to observe your fish carefully because my fish never showed any signs, not even spots, but I did see them scratch themselves on rocks so sometimes that could be the only sign. Even netting a fish with Ich, then using that net on another tank, could introduce this nasty parasite, so I sterilize all equipment before bringing it back to the main tank.

    Contributed by Sam Krienke

    In this article on using heat to treat ich, it is suggested that CO2 injection should be discontinued while the water temperature is raised to 32C. However, in a heavily planted tank, simply shutting off the CO2 may lead to the rapid growth of algae, and swings in pH. In this situation, especially where visible oxygen bubbles are being produced by the plant, discontinuing CO2 may not necessary, and may be harmful to the overall health of the tank.

    Contributed by Scott Garbus

    A terrific article on how to treat Ich. I've a heavily planted tank with CO2 being added, filtration but no aeration. I've got tetras and corys in the tank, both of which are supposedly sensitive to salt. I use a combination of Stress Coat, increased temperature (my normal is 28C but I bump up to 30C for tx), salt started at 1 tablespoon per 20 liters with another 1 Tbsp/20 L added slowly over the next day or so, and twice daily doses of Ich Attack. As long as the salt is increased slowly, the corys seem to tolerate it, although they tend to get buoyant and have trouble staying on the bottom of the tank. My local aquarium stores seems to have endless problems with Ich, but they're the only place around, so I've gotten really good at dealing with the problem!

    Contributed by Sandra More

    I had a bad a outbreak of Ich in a 29 gallon tank with giant danios, neon tetras, black neon tetras, lemon tetras, long finned rosy barbs and a cory cat. The Ich hit the neons very hard. It didn't infect the others too much and the cory cat and lemon tetras not at all. I turned heat to 32C for 7 days. The fish seamed to love it. Ich worsened significantly for about 3 days (to be expected) then started to disappear. By day seven it was nearly gone. Then I added 1 tsp of salt per 4 liters of water and Ich was completely gone in 2 more days. The fish seem to love the salt as well. A week later Ich was reintroduced by a couple of new neons (I swear they looked clean in the store! As soon as I released them in the tank I noticed two white spots...doh!). I just kept the salt and heat the same and it's already moving out of their system 3 days later. I'm not in a big hurry to lower heat or remove salt as the fish seem to do well with it.

    Contributed by Clay Butler

    The following information relates to African Cichlids. This treatment is for fully cycled aquariums only.
    Step 1: Do a large water change, 50% and remove carbon from all filters.
    Step 2: Increase temperature to 33C and increase aeration. Your cichlids will handle this with ease.
    Step 3: Use Aquarisol 12 drops for every 40 liters of water. Repeat daily for 7 days. If your cichlids show distress (not likely) do a 50% water change and resume treatment.
    Step 4: Day 7. Continue treatment with Aquarisol and add salt, 1 tblsp for every 20 liters of water.
    Step 5: Day 8. Continue treatment with Aquarisol and add salt, 1 tblsp for every 20 liters of water.
    Step 6: Continue treating with Aquarisol up to day 10.
    Step 7: On day 11 change 50% of the aquarium water and replace with conditioned water with salt, 2 tblsp per 20 liters.
    Step 8: On day 11 change 50% of the aquarium water and replace with conditioned water with salt, 2 tblsp per 20 liters. Return filter carbon to remove the last of the Aquarisol.
    Step 9: Slowly decrease your heat to 31C and leave the salt in the aquarium for another 10 days.

    Follow these steps and your cichlids will be disease free and healthy! This method is what I have used for the past 25 years and has worked flawlessly for me. The only fish losses I had were from new aquariums that were not fully cycled. If your aquarium is not cycled and you start treatment for Ich, I wish you luck. I hope this helps!

    Contributed by Steve

    I have had fish over 38 years. That doesn't mean I know it all, however having had experience dealing with Ich and other diseases, I hope my method helps you out, as it has been 100% effective for me.

    I heat to 30C, gradually, over a 3 day period of time. I add 1 teaspoon of salt per 4 liters the first day (this must not be done in a planted tank, as most plants are not salt tolerant), and half a teaspoon of salt per 4 L the second day, and half a teaspoon of salt per 4 L the third, totalling 2 teaspoons of salt per 4 L. Parasites should be dead, non productive and over with, completely, within ten days treatment.

    When lowering heat back down, gradually reduce by no more than 1C an hour, until fish are comfortable, as over a 10 day period of time, the fish can become very acclimated, and you can shock them by returning them to colder water without acclimation.

    Ultimately, THE BEST WAY to cure Ich is to leave the tank empty for one month, with no fish and to heat it to 28C during the duration of this time, so that all Ich develop, morph into adults, and die off without hosts. Happy fish-keeping!

    Contributed by FishDeeva

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