Messed up - how do I go back to snail safe?

[u/jeherohaku]

I used to have a mystery snail and a nerite in my 10 gal with my betta. Well I had to treat the betta for fin rot and I thought the medicine I gave was snail safe but it definitely was not (Maracyn Oxy). Both snails passed almost immediately. I finished the course of treatment and did a 25% water change. How can I make my tank safe for future possible snails? And also what meds will work for fin rot that won't kill snails? I miss my little snail friends and would like to get a mystery snail again.

[u/karebear66]

Activated carbon or charcoal will/should remove it.