White spot is a protozoan parasite; the adults live on the fish and appear as tiny white spots. The adult has a complex life cycle which results in hundreds of free-swimming juveniles looking for a host fish to infest.

Use when small white spots, like grains of salt, can be seen scattered on the body of the fish, if the fish are showing signs of irritation and rubbing on objects in the aquarium, fish have a grey, velvety film all over the body, or fish have white cotton wool-like growths on their body/mouth/ fins.