No planaria and filter

Hi guys. Looking for some advice. Ive started a new tank with all new new stuff. Cycling it. Problem. Old tank had snails. Kept the good filters in it. Which I need for the new tank. Ive kept them alive with ammonia. Ok heres the question: I poisoned it with No Planaia. How do I know if the snails (very small) are dead in the filters? I really don't what to add new filter media. I don't want to lose the good bacteria in them. Thanks for any info :)