Ich (White Spot) in Aquarium Fish: Treatment Guide

Quick answer

Ich (white spot disease) is a common parasite that leaves small white dots, like grains of salt, on a fish's body and fins. It spreads to every fish in the tank. Treat the whole aquarium, usually with an ich medication or another method that suits your species. Keep going until several days after the last spot has gone, and sort out whatever stress or new arrival set it off.

What is ich?

Ich (or "ick") is caused by a single-celled parasite, Ichthyophthirius multifiliis, which infects freshwater fish. Marine fish get a different parasite that looks much the same (Cryptocaryon, often called marine white spot), and it needs different treatment. This guide covers freshwater ich.

The parasite is everywhere in the hobby. It usually arrives with new fish, plants or water from another tank. Healthy fish in good water may fight it off, but stress makes an outbreak more likely: a new tank, poor water, temperature swings or transport.

How to recognise it

• Small, raised white spots, roughly the size of salt or sugar grains, on the body, fins or gills.
• Fish rubbing or "flashing" against decorations, gravel or the glass.
• Clamped fins, lethargy, hiding or loss of appetite.
• Rapid breathing or gasping at the surface, especially when gills are infected.

Not every white spot is ich. Bigger, cotton-like tufts may be fungus. White spots on the head of a male goldfish in breeding season can be normal breeding tubercles. A few other parasites look similar too. If you're not sure, ask a fish vet or an experienced aquarist to look at a clear photo.

Why the life cycle matters

The life cycle is the reason ich treatment fails so often.

In warm tropical water one full cycle takes a few days; in cool water it takes much longer. Medication only kills the free-swimming stage, so you have to keep treating long enough to catch each generation as it hatches.

Treatment steps

Treat the whole tank, not just the fish with spots. Taking one fish out leaves the parasites behind in the water.

1. Test the water. Check ammonia, nitrite, nitrate and pH. Bad water weakens fish, so fix it first. See The Aquarium Nitrogen Cycle, Explained Simply.
2. Do a partial water change and vacuum the gravel. This lifts some of the cysts out of the substrate.
3. Increase aeration. Infected gills and warmer water both make oxygen more of a concern.
4. Choose a treatment that suits your fish. Options include:
   • Commercial ich medications sold for aquarium use. Follow the label exactly, dose and duration included. Some aren't safe for scaleless fish (many catfish and loaches, for example), invertebrates (shrimp, snails) or certain plants, so check before using one.
   • Gradual temperature increase for tropical fish that can take it. Warmer water speeds up the life cycle, so the parasites hit the vulnerable stage sooner. It's usually used alongside medication rather than on its own, and it isn't suitable for cold-water fish or heat-sensitive species.
   • Aquarium salt is used by some keepers for salt-tolerant freshwater fish. Many species and plants don't tolerate it, though, so only use it with advice specific to your species.
5. Remove activated carbon from the filter during treatment, because it can soak up medication. Keep the filter itself running.
6. Continue treatment for the full course on the label, and until at least several days after the last white spot has gone.
7. After treatment, do a water change, put carbon back if you use it, and keep watching in case it returns.

Don't mix different medications, and never go over the label dose. If you're unsure, a fish vet or aquatic specialist can advise you and help with dosing.

What a fish vet typically does

With valuable fish, big collections or an outbreak that isn't getting better, an aquatic vet can confirm the diagnosis by looking at skin or gill scrapes under a microscope. They can also check for other infections and suggest a treatment plan that is safe for your species and setup. Follow your vet's dosing exactly.

Prevention

Quarantine is the big one. Quarantine all new fish in a separate tank for a few weeks before they go into your main aquarium; nothing keeps ich out more reliably. Buy healthy fish, too, and walk away from tanks with spotted, flashing or dead fish in them, even if the fish you want looks fine.

• Avoid adding shop water to your tank when you release new fish.
• Keep water quality stable: regular partial water changes, no overfeeding, no overstocking.
• Avoid temperature swings: a reliable heater for tropical fish, and no tanks in draughts or direct sun.
• Disinfect or dedicate nets and equipment between tanks.

When to see a vet

Get expert help, from an aquatic vet if there is one near you, if:

• fish are gasping at the surface or breathing rapidly despite good aeration;
• several fish are dying;
• spots are not improving after a full course of treatment;
• you see other symptoms, such as cottony growths, ulcers, red streaks or frayed fins;
• you keep sensitive species (scaleless fish, invertebrates, delicate wild-caught fish) and are unsure what treatment is safe.

Caught early and handled properly, ich is very treatable. If you keep goldfish, our Goldfish Care Guide covers the cold-water setup in more detail. When you buy new fish, pick healthy stock from verified sellers; you can browse fish on Paalo.