If you are here because a fish looks wrong, start by reading the symptoms rather than reaching for a bottle. A large share of what gets medicated is not an infection at all, and medicating a water-quality problem makes it worse by damaging your filter bacteria.
Test the water first
Ammonia or nitrite above zero will produce clamped fins, rapid breathing, lethargy and reddened gills — symptoms easily mistaken for disease. If either reads above zero, the treatment is water changes, not medication. Bring us a sample and we will test it free.
Reading the common problems
Ich presents as distinct white spots like grains of salt on the body and fins, usually with flashing against decor beforehand. It has a life cycle, and it is only treatable at one stage, which is why treatment must run the full course even after spots disappear.
Velvet is a fine gold or rust dust, easiest to see with a torch held at an angle, and it moves faster than ich.
Fin rot recedes from the fin edge inward with a dark ragged margin, over days. It is a water-quality problem first and an infection second.
Fin biting looks like rot but takes clean semicircular chunks out overnight with no dark margin. Medication does nothing for it — it is stress or boredom, and long-finned fish do it most.
Fungus is white cottony tufts, usually on an existing injury. Dropsy is a swollen body with scales standing out like a pinecone, and it is a symptom of organ failure rather than a disease in itself.
Quarantine, and mind the invertebrates
Treat in a separate tank wherever you can. Most medications damage the bacterial colony in your filter, and many contain copper, which is lethal to shrimp and snails at doses fish tolerate easily. Remove carbon from the filter during treatment — it strips the medication straight back out.
Finish the full course even once the fish looks better, and do not combine medications unless the labels say you can.
Not sure what you are looking at? Bring us a photo or a video. We would rather tell you it is nothing than sell you a bottle you do not need.
