Ich is a protozoan parasite with three stages to its lifecycle.
Stage 1 is on the fish where we see it as the white spot. In this stage it eats the fish's tissues. When it's eaten enough it falls of and the spot disappears.
Stage 2 is where it sits on the bottom of the tank in a sort of cyst and multiplies.
Stage 3 is where the cyst opens and hundreds of new parasites go swimming off looking for a fish to infect.
The parasite can only be killed in stage 3, whether by heat or medication, as the coating protects it in stages 1 and 2. This is why the temperature is kept at the higher level for 2 weeks, and why medication says to add on certain days even after the spots have gone. If even one cyst hasn't opened when the temp is lowered or the medication is stopped, the fish will be reinfected.
Stage 1 is on the fish where we see it as the white spot. In this stage it eats the fish's tissues. When it's eaten enough it falls of and the spot disappears.
Stage 2 is where it sits on the bottom of the tank in a sort of cyst and multiplies.
Stage 3 is where the cyst opens and hundreds of new parasites go swimming off looking for a fish to infect.
The parasite can only be killed in stage 3, whether by heat or medication, as the coating protects it in stages 1 and 2. This is why the temperature is kept at the higher level for 2 weeks, and why medication says to add on certain days even after the spots have gone. If even one cyst hasn't opened when the temp is lowered or the medication is stopped, the fish will be reinfected.