Recognizing symptoms
The clearest sign is small, white spots (roughly 0.02–0.06 in) that first appear on the fins and spread across the body over time. Affected fish often scrape themselves against rocks or decor to relieve itching.
Why does the disease break out right now?
The pathogen is present latently in almost every aquarium without causing an outbreak — similar to how some cold viruses work in humans. Only once the fish's immune system is weakened, for example by the stress of transport, new water conditions, or poor water quality, can the parasite spread.
Why treatment takes several days
Treatment
Raise the temperature carefully
Raise to around 82–86°F (depending on species) — this speeds up the parasite's life cycle. Important: add extra aeration, since warmer water holds less oxygen.
Salt treatment (optional, for salt-tolerant stocking)
Add gradually, following product guidance for your water hardness — split into several small additions over 24 hours to protect filter bacteria.
Use a dedicated medication
Commercial ich treatments from a pet store, dosed per the label. Invertebrates like shrimp often can't tolerate many of these treatments — check first.
Follow through with the full treatment
Keep treating even after visible spots disappear, since free-swimming stages may still be active in the water.