Photo: D. Herdemerten (Hannibal21) · CC BY 3.0
husbandry · freshwater
How to treat ich: cure white spot in freshwater fish
To treat ich, also called white spot disease, test the water, pull the carbon out of the filter, and dose one malachite-green or formalin ich medication for your real gallon count. Raise the heat into the upper 70s to low 80s F only if your fish can take it, and add air when you do. Keep treating for several days after the last white spot is gone, or it comes back.
By Fishy Dave · Published 2026-09-03 · Updated 2026-10-07
To treat ich, also called white spot disease, test ammonia, nitrite, and nitrate and fix the water first. Pull the carbon out of the filter, then dose one malachite-green or formalin ich medication for your real gallon count. Raise the heat into the upper 70s to low 80s F only if your fish can take it, and add air when you do. Keep treating for several days after the last white spot is gone, or it comes back.
The ich life cycle, and why you treat after the spots are gone
Freshwater ich is the protozoan Ichthyophthirius multifiliis. The white spots you see are trophonts under the skin. Those stages are protected. Medication works on free-swimming theronts after the parasite leaves the fish. That is why you finish the course days after the last spot, not the day the tank looks clean.
At typical tropical temperatures the life cycle runs in a few days. Cooler water stretches it. Marine white spot is a different organism (Cryptocaryon). This page is freshwater only.
Confirm it is ich
Classic ich looks like fine salt grains scattered on body and fins. Fish often flash on décor, clamp fins, or breathe hard when gills are involved. Epistylis can look similar but often sits on a wound and looks fluffier. Lymphocystis makes larger cauliflower lumps, usually on fins, and is viral, not an ich bottle problem.
If ammonia or nitrite is up, fix water quality first. Medication on top of a dirty tank is theater. Ich often shows up in a tank that never finished cycling or right after new fish go in. Test, change water if needed, then treat the parasite.
Temperature, meds, and salt
Raise temperature only if the species and oxygen allow it. Bettas tolerate warmth; many tropical community fish sit fine in the upper 70s to low 80s F for treatment. Extra aeration helps because warmer water holds less oxygen. Do not force a coolwater fish or a stressed, gasping tank into a heat experiment. Neon tetras can take a short bump, but bring them back to the mid-70s once treatment ends. A thermometer beats the heater dial.
Malachite-green or formalin ich medications are the usual path. The ich medication and aquarium salt page compares the two bottles we use and their label doses. Remove chemical filtration (carbon, Purigen, and similar) so the med stays in the water. Dose for the actual gallons. Do not mix random bottles. Follow one label to the end, including the days after spots vanish.
Aquarium salt is optional. Some keepers use it as a support; it is hard on scaleless fish (corydoras, many catfish), live plants, and shrimp. Skip salt in a planted community or a cory tank unless you know those livestock tolerate it. Salt is not a reason to skip a labeled medication when the infection is clear.
How to treat ich, step by step
1. Test ammonia, nitrite, and nitrate. Correct water quality if needed with a partial water change. 2. Remove carbon and other chemical media. 3. Decide whether a modest temperature bump is safe for your fish; add air if you raise heat. 4. Dose one ich medication per the bottle. 5. Keep up water changes the label allows. 6. Continue several days after the last spot. 7. When you are done, replace chemical media if you use them.
Quarantine new fish when you can so the display tank is not the hospital. A bare 10-gallon quarantine tank doubles as the place to treat one sick fish. If only one fish is sick in a large community, treat the tank anyway. The theronts are already in the water. Heat-only is not a guarantee. Finish the course.
Gear for treating ich
A few listings we would open for this job. Skip anything you already own that still works.
Aqueon Pro adjustable heater, 100W
Stable heat matters during treatment. Raising temperature only works if the species and oxygen allow it. A reliable adjustable heater is how you hold a target, not a guess.
Use 50W on a 10-gallon. Do not cook a coolwater fish. Extra aeration helps if you raise temperature. Skip a second heater if one unit already holds the number.
See this listingPAIZOO stick-on digital thermometer
You cannot treat by dial alone. Stick-on digital read outside the glass tells you whether the heater is actually holding the temperature you chose.
Place it away from the heater. A clip-on glass thermometer is fine if you already have one.
See this listingAPI Liquid Super Ick Cure, 4 oz
A widely available malachite-green freshwater ich medication. Remove carbon, dose the bottle, and finish the course after the last spot. One product. Do not cocktail.
Follow the label for your gallon count. Not a shrimp tank product. Skip this if you already have a malachite-green/formalin ich med in date and are mid-course. This is freshwater ich, not marine Cryptocaryon.
See this listing
Frequently asked questions
How do you treat ich in fish?+
Test ammonia and nitrite and fix them first. Remove carbon and other chemical media, then dose one labeled ich medication (malachite green or formalin) for the actual water volume. Raise the temperature a few degrees if the species tolerates it, add aeration, and treat the whole tank, not just the spotted fish.
How long does ich treatment take?+
Plan on at least a week at tropical temperatures, and longer in cooler water because the life cycle slows down. The bottle sets the dosing schedule. Whatever it says, keep going for several days after the last spot drops off, because the parasites that just left the fish are still in the water.
Should I raise the temperature for ich?+
Only if your fish can handle it. A bump into the upper 70s to low 80s F speeds up the life cycle so the medication reaches the free-swimming stage sooner. Warm water holds less oxygen, so add an air stone. Skip the heat for coolwater fish or a tank that is already gasping. Heat alone is not a reliable cure.
Does salt cure ich?+
Not on its own, and not in every tank. Aquarium salt is hard on corydoras and other scaleless fish, live plants, and shrimp. Some keepers use it as a support in a hardy, plant-free tank. A labeled ich medication is the default when the spots are real.
Can fish recover from white spot disease?+
Yes. Most fish recover fully when you catch ich early and finish the course, and the skin clears once the parasites leave. Heavy gill infections are the dangerous cases. Watch for fast breathing at the surface and keep the water well aerated while you treat.
What does ich look like?+
Salt-grain white spots on body and fins, often with flashing (rubbing on decor), clamped fins, or rapid breathing. Spots that look fuzzy, large, or sit only on one wound are often something else.