White spots on fish: how to treat ich

Small white dots that look like grains of salt on a fish's body and fins are almost always ich (white spot disease). It's the most common fish parasite, and it's very treatable if you start early and finish the treatment.

Is it ich?

Ich looks like someone sprinkled salt on your fish. The spots are all about the same size and can show up anywhere on the body, fins and gills. Fish with ich often:

• Rub or "flash" against rocks, gravel and decorations
• Hold their fins close to their body
• Breathe faster than normal, or hang near the surface
• Hide or stop eating

Things that look like ich but aren't:

• Fluffy, cotton-like patches are more likely fungus or a bacterial infection, which need a different treatment.
• A fine gold or rusty dust, easiest to see with a flashlight, is velvet, a different parasite.
• Small white bumps on a male goldfish's gill covers and front fins in spring are breeding stars. They're normal.
• One or two larger white lumps that don't spread are usually something else. Ich spreads to many spots quickly.

Why treatment takes a while

The white spots are the parasite sitting under the fish's skin, where medicine can't reach it. After a few days each one drops off, settles on the gravel or glass, and splits into hundreds of tiny swimmers that look for a fish to attach to. Medicine only kills those free-swimming babies.

That's why you have to keep treating after the spots have gone. Warmer water speeds up the life cycle, so the treatment finishes sooner.

How to treat ich, step by step

1. Test your water. Ich usually takes hold when fish are stressed. If ammonia or nitrite is above zero, do a water change first.
2. Treat the whole tank. If one fish has spots, the parasite is already in the water. Moving one fish out doesn't solve it.
3. Raise the temperature slowly to about 80–82°F, by no more than about 2°F a day, as long as all your fish are comfortable that warm. Skip this for cold-water fish such as goldfish and white cloud minnows, and just follow the medicine label.
4. Add aeration. Warm water holds less oxygen, and some medicines lower it further. An air stone helps.
5. Take carbon out of the filter. Carbon removes medicine from the water. Leave the rest of the filter running.
6. Dose an ich medicine exactly as the label says. Many labels ask for a water change and a gravel vacuum before each new dose. That also sucks up the parasites waiting on the bottom.
7. Keep going after the last spot is gone. Continue for at least 3 more days, or as long as the label says, to catch the last of the swimmers.
8. Bring the temperature back down slowly and put fresh carbon back in if you use it.

Shrimp, snails and loaches: many ich medicines are risky for shrimp and snails, and scaleless fish such as loaches can be sensitive to a full dose. Check the label before you treat. If it isn't safe for them, move them to another tank until the treatment is over.

How to stop it coming back

• Quarantine new fish for a few weeks before they join your main tank. This is the single best way to keep ich out. See how to set up a quarantine tank.
• Never pour store water into your tank. Net the new fish out of the bag instead.
• Keep the temperature steady with a heater and thermometer. Sudden drops are a common trigger.
• Keep the water clean with weekly water changes. Stressed fish catch ich more easily.

Related: How to set up a quarantine tank · Why are my fish dying? · Fish gasping at the surface