Small white spots that look like grains of salt or sugar scattered across a fish's body and fins are the classic sign of ich (short for Ichthyophthirius multifiliis), one of the most common freshwater fish parasites. It spreads quickly through shared water, so the whole tank needs treatment, not just the fish that's visibly spotted.
Is ich contagious to other fish?
Yes. By the time you see white spots on one fish, the parasite's free-swimming stage is very likely already present elsewhere in the water, even on fish that look completely clean. Treating only the visibly affected fish, or moving it to a separate tank while leaving the rest of the display untreated, is the single most common mistake people make with ich.
What causes an ich outbreak?
- Stress from a sudden temperature change, transport, overcrowding, or a recent move weakens a fish's immune response and lets the parasite take hold.
- New arrivals — fish, plants, or decorations added without a quarantine period are the most common way ich enters an established tank.
- Cooler water slows the parasite down but also lets it linger longer, which is part of why outbreaks are common during seasonal temperature swings.
How do you treat ich?
- Raise the tank temperature gradually to around 82-86°F (28-30°C). This speeds up the parasite's life cycle so medication can actually reach it during its vulnerable free-swimming stage.
- Treat the entire tank with a dedicated ich medication or aquarium salt — not just the fish with visible spots.
- Continue the full course of treatment listed on the product, even once the spots disappear. Visible spots clearing doesn't mean the parasite's life cycle is finished.
- Quarantine any new fish for 2-4 weeks before adding them to your main tank going forward, to avoid reintroducing it.
How long does ich take to cure?
Most treatments take 7-14 days to fully clear an outbreak. That's longer than most people expect, and it's specifically because part of the parasite's life cycle — the stage where it's encysted on the tank bottom or decor, not on the fish — is resistant to medication. Stopping treatment early because the fish "look better" is why ich often seems to come back a week later; it didn't come back, it was never fully gone.
Ich vs. other white spots — how to tell the difference
| What you're seeing | Likely condition |
|---|---|
| Tiny, uniform white dots, salt-grain sized, spread across body and fins | Ich |
| Fish also rubbing/scratching against rocks or decor | Ich (a very common companion symptom) |
| A single larger white patch or cottony growth | Likely a fungal infection, not ich |
| White edges specifically on fins, not the body | More likely fin rot — see our fin rot guide |
If you're not fully sure what you're looking at, run the 2-minute fish diagnosis — it separates ich from fin rot and other look-alikes based on your fish's exact symptoms, and links straight to the full ich treatment guide with step-by-step fixes.