Snail treatments freqently kill other fish and upset the balance of the tank. Also, the water changes required to get rid of the product end up wiping your tank clean, which means it pretty much needs to be re-cycled. In the future, you might want to consider quarantining the fish in a seperate tank before treating the water, or just getting clown loaches, that love eating snails. For now, you might want to consider moving your fish to a secondary tank with new water (you can add tap water conditionner and a cycle product to soften the blow) until your primary tank can be recycled. Also, if the snail infestation is really bad, you will probably have to manually remove the snail carcasses from the gravel;otherwise, they will decompose and upset the water balance.
I know how frustrating snail infestations can be. After years without problems, I recently developped a massive snail infestation in my 50G tank that clogged the filters. I'd clean out the tubes and a few hours later they'd be clogged again. When my fish started dying off, I quarantined the survivors and started the tank over a gain. I tried boiling the gravel to kill the snails and picked nearly 2 full cups of snail carcasses out of only a third of the gravel before calling it quits. In the end, I replaced the gravel and all the plants, boiled the driftwood to kill any eggs, did a compte water change, cleaned the filter, treated the empty tank with a snail-removing product and let the filter run for a week without the charcoal, did a 2nd complete water change and let the filter run for a week with the charcoal, changed the charcoal (to remove any trace of anti-snail product), cleaned the filter again, did a 3rd compete water change and let the tank run for a week before adding plants and a few hardy fish to get it cycling, then starting reintroducing the survivors. This was, however, a radical infestation. Now, I have 3 clown loaches to help keep this from happening again : )
Prevention is the best remedy, so make sure to soak newly purchased plants in some salt water and rinse them thoroughly before introducing them to your tank, and don't add the water from newly purchased fish to your tank (can contain snail eggs). What I do after floating the bag my fish came and gradually filling the bag with tank water to acclimatize the fish, I net the fish one by one and "rinse" them by gently pouring tank water (which by this point they're used to) over them while holding the net over a bowl, then I release them into the tank. It seems to be working.
Best of luck!
