With Ich we are treating the tank, not the fish, so all effective treatments are designed to kill the trophite form of the disease while it is in the tank. The mature ich organisms that cause the problems on the fish do not die from treatment, but fall off in a couple of days during their normal life cycle and then their offspring die from the treatment in the water.
Lets try to explain better,,,you buy a new fish,plants etc,,, you get just 1 Ich paracite,,,ok this paracite injects eggs into fish,,,egg sac is what you see on fish,,,this sac falls off more paracites inject fish.
You have to kill paracites when they fall off, the medication only kills live paracites not eggs.
I have never stressed more about having a small hospital tank and quarantine tank.
Anyway quarantine all fish, snails etc, anything that lives.
do not treat main tank as the paracites will be dead within a couple of days (nothing to attach to)
Treat hospital tank,,,we use a copper based treatment,,use with caution following instructions as copper is poisonous to fish, keep in hospital tank for 7 days, put your fish into quarantine for 7 days before moving them back to main tank. Remember to quarantine anddo not put then straight into tank as the fish feaces can contain paracites, but the 7 day treatment usually clears everything.
Hope this helps