01
What is ich (ick) on fish?
Ich, also spelled ick and called white spot disease, is caused by Ichthyophthirius multifiliis, a single-celled parasite that burrows into the skin and gills of freshwater fish. Each white dot you see is a parasite sitting under a thin layer of skin, where medication cannot reach it. That is the key to every ich treatment in an aquarium: you are not killing the spots, you are killing the free-swimming stage that comes after them.
Ich is common because it rides in on new fish, plants and even water from a store bag, then strikes when fish are stressed by a temperature drop, poor water or a recent move. A healthy, well-cycled tank with stable conditions rarely has outbreaks. If you are still setting up, read how to cycle a fish tank first, because fish in uncycled water are far more vulnerable.
02
Symptoms: how to identify ich
The classic sign is a scattering of raised white dots, roughly the size of a grain of salt (about 0.5–1 mm), on the body and fins. Gills can be infected before any spot shows on the skin, so rapid breathing can come first.
- Flashing: fish rub or dart against rocks, gravel and decor
- Clamped fins, hanging near the surface or near the filter outflow
- Fast gill movement, gasping at the surface in heavy gill infections
- Loss of appetite and lethargy as the disease progresses
| What you see | Likely cause | How to tell |
|---|---|---|
| Distinct white dots like salt, spreading over days | Ich (white spot) | Dots are round and separate, fish scratch and clamp fins |
| Fine gold or rust-colored dust, best seen with a flashlight | Velvet (Oodinium) | Much smaller than ich spots, coat looks powdery |
| White dots only on gill covers and front fins of a male goldfish | Breeding tubercles | Appear in spring, no scratching, fish acts normally |
| Larger white tufts or cotton-like patches | Fungus or columnaris | Fluffy or patchy, not salt-like dots |
| Lumpy, cauliflower-like growths | Lymphocystis (viral) | Few large clusters, slow to change |
03
The ich life cycle and why timing matters
Ich has three main stages. The feeding stage (trophont) lives under the skin and is protected. When mature, it drops off the fish and forms a cyst (tomont) on the gravel, plants or glass. Inside the cyst it divides into hundreds or thousands of free-swimming tomites, which must find a fish within roughly one to two days or die.
Medication and salt only work on the free-swimming stage and, to a lesser extent, on the cysts. Temperature controls the speed of the whole cycle: about a week at 77 °F (25 °C), faster in warmer water and several weeks in a cold goldfish tank. This is why ich treatment always runs for days, why it fails when stopped early, and why the spots often look worse during the first two or three days of treatment.
04
Ich treatment step by step
Treat the main tank, because the cysts and free-swimming stages are already in it. A separate hospital tank only makes sense for a single precious fish or for species that cannot take the medication. If you keep cherry shrimp or snails, plan where they will go before dosing anything.
- Test the water: ammonia and nitrite must read 0 ppm. Fix them first with a water change and a dechlorinator from our best water conditioner guide.
- Remove activated carbon or chemical media from the filter, since it absorbs medication.
- Raise the temperature slowly, about 2 °F (1 °C) every 12 hours, to 82–86 °F (28–30 °C) for tropical fish that tolerate it. Use a reliable unit from our aquarium heater reviews. Do not push goldfish or cool-water species past about 77 °F (25 °C).
- Add aeration with an air stone, because warm water holds less oxygen and ich damages the gills.
- Dose a proven ich medication following the label exactly, including any reduced dose for scaleless fish such as loaches and corydoras.
- Vacuum the gravel lightly and change 25–30% of the water before each new dose if the label allows it; this removes many cysts.
- Continue for several days after the last spot disappears, then return the temperature to normal gradually and put the carbon back to remove leftover medication.
Most ich medications based on malachite green, formalin or copper can kill shrimp and snails and stress sensitive fish. Move invertebrates out, or choose a product labeled invertebrate-safe, and never combine two medications.
05
Which ich medication to use
In the US, widely sold options include Hikari Ich-X (formalin and malachite green), Kordon Rid-Ich Plus, API Super Ick Cure and Seachem ParaGuard, a gentler aldehyde-based product. All are effective when used for the full course; the label always overrides any general advice, including this guide.
Salt is a classic alternative for fish that tolerate it, especially in livebearer and goldfish tanks, but it harms scaleless fish and many plants. Our page on aquarium salt uses explains when salt helps and when to avoid it. Heat alone at the upper end of the range is sometimes used, but heat plus a medication is more reliable.
06
Ich in bettas, goldfish and sensitive species
Bettas tolerate 82–84 °F (28–29 °C) well, so heat plus a half-strength or label-approved dose usually clears ich quickly in a heated, filtered tank. See our betta fish care guide for normal conditions to return to afterwards.
Goldfish are cool-water fish, the cycle runs slower and treatment takes longer, often two to three weeks. Keep the temperature moderate and rely on medication and water changes; our goldfish guide covers their normal range. Tetras, loaches, catfish and fish like the neon tetra are sensitive to strong medications, so watch them closely during the first doses.
07
How to prevent white spot disease
Ich almost always arrives with new fish. A simple quarantine tank (a 5–10 gallon tank with a heater and a seeded sponge filter) where new fish spend 2–4 weeks before joining the main aquarium stops most outbreaks. Our best sponge filter page lists models suited to quarantine.
Avoid sudden temperature drops during water changes and power cuts, keep water quality steady with a regular water change routine, and do not move gravel, plants or nets from an infected tank to a clean one without drying or disinfecting them.
08
When to call an aquatic vet
Call an aquatic veterinarian if fish are gasping heavily, if they keep dying despite correct treatment, or if spots return right after a full course. A vet can take a skin and gill scrape, confirm ich or rule out velvet, flukes or bacteria, and advise on treatment for valuable fish. Also stop medicating and do a large water change if fish show distress shortly after a dose.
Frequently asked questions
Frequently asked questions
How long does it take to treat ich in fish?
In a tropical tank at 82–86 °F (28–30 °C), most outbreaks clear in 7–14 days. In cooler water, such as goldfish tanks, it often takes two to three weeks because the life cycle is slower. Keep treating for several days after the last visible spot disappears, as the label directs, or survivors in the gravel will start a new wave.
Can ick on fish go away on its own?
Occasionally a mild case in a healthy, stable tank fades without treatment, but it is risky to wait. Each spot releases hundreds of new parasites, so numbers can explode within a week, especially in a crowded tank. Early treatment is shorter, gentler and much more likely to save every fish.
Do I need to treat the whole tank for ich?
Yes. When you see spots, the parasite is already in the tank as cysts and free-swimming stages, and every fish has been exposed. Treating only the visibly sick fish in a separate tank leaves the source untouched. Move invertebrates out if the medication is not labeled safe for them.
Is ich treatment aquarium medication safe for shrimp and snails?
Most ich medications containing malachite green, formalin or copper are harmful to shrimp and snails. Move them to a separate tank during treatment, or pick a product whose label states it is safe for invertebrates. Leave them out until the medication has been removed with water changes and fresh carbon.
Can ich come back after treatment?
It can, usually because treatment stopped too early or new fish brought it in again. Some fish also carry low-level infections that flare up under stress, such as a temperature drop. Finishing the full course, quarantining new arrivals and keeping temperature stable are the best ways to stop repeat outbreaks.
Sources and references
Written and reviewed by the handsoffmyhobby editorial team according to our editorial policy.
