The short answer
Ich (short for Ichthyophthirius, also called white spot disease) is one of the most common parasites in freshwater aquariums. It shows up as tiny white, salt-like spots on a fish’s body, fins and gills, and is usually triggered by stress or a temperature swing that lets the parasite take hold. It’s treatable, but the safest path is to check your water first, then research a proper treatment and get advice before dosing anything.
What ich looks like and why it appears
The classic sign is scattered white dots, like grains of salt or sugar, often alongside flicking or rubbing against decor, clamped fins and faster breathing. The parasite has a life cycle that includes a free-swimming stage in the water, which is why it spreads and why treatment takes time.
Outbreaks almost always follow a stress trigger: a chill from a broken heater, rough shipping, poor water quality, or new fish added without quarantine. A healthy, low-stress fish in stable water resists it far better.
General management (not a prescription)
Common, widely-recommended supportive steps include raising the temperature gradually to speed up the parasite’s life cycle, keeping the water spotless with regular changes, and using a recognised white-spot treatment. Exact temperatures, products and doses depend on your fish and plants — some species and invertebrates are sensitive — so research a treatment suited to your tank and ask a vet or experienced fishkeeper before you dose.
This is general information, not a diagnosis or treatment plan. When in doubt, get eyes on the fish from someone experienced.
Prevention beats treatment
The reliable way to avoid ich is a stable, cycled tank and a quarantine period for every new fish — see do I need to quarantine new fish? and our guide to a fishless cycle. Steady temperature, clean water and calm surroundings keep the parasite from ever getting a foothold. For related symptoms, see why does my fish have white spots?