I recently bought a few apple snails (medium sized) for a 20 gallon tank. I thought they would eat all the leftovers my fish doesn't eat. Anyway, the problem is, everytime I wake up, I see a lot of gunk all over the tank. It's stringy and wavy and it seems like something I would find in the bottom of my filter. It's not green but gray so I don't think it could be algae. It's persistent and I see this every morning all over my tank. It also seem to grow near or attached to large rocks. I was wondering if anyone knows if I could blame my snails for this? Thanks in advance. 
