To get rid of ick, you need to keep treating even after the spots are gone.
When it disappears each spot erupts into @ 100 larval ick which fall into the substrate.
These are programed to hatch at different intervals, some take a day, some could take two weeks.
The warmer the tank water, the faster they "can" hatch out (in theory). When they hatch is when they are vulnerable to salt, and/or other meds.
So it is often necessary to treat for a few weeks after all the spots have erupted off the fish, and do lots of water changes, with vacuuming of the substrate to eliminate the dormant larval protozoa in the substrate, before they hatch out to again infect a fish.
Just like when a Dr tells you to take an antibiotic until it is used up, or face a relapse.
When it disappears each spot erupts into @ 100 larval ick which fall into the substrate.
These are programed to hatch at different intervals, some take a day, some could take two weeks.
The warmer the tank water, the faster they "can" hatch out (in theory). When they hatch is when they are vulnerable to salt, and/or other meds.
So it is often necessary to treat for a few weeks after all the spots have erupted off the fish, and do lots of water changes, with vacuuming of the substrate to eliminate the dormant larval protozoa in the substrate, before they hatch out to again infect a fish.
Just like when a Dr tells you to take an antibiotic until it is used up, or face a relapse.