I removed my snails and they're in a much smaller container, and I really need to get them back in because my nerite and rabbit snails both managed to escape and die. The tank I removed them from was dosed with fenbendazole a few weeks ago, but it's a shrimp tank so I haven't been doing large water changes, just smaller daily ones. Does it dissapate after a while? I can't use carbon as I have a sponge filter. After the number of water changes I've done, 32.6% of the original water dosed remains. How low does this need to be if it doesn't go away on its own?