Homemade Carbon Filter
 

I put some snails in at week two of a 20 gallon startup and they did fine for a few hours then dropped off the glass and stopped moving. I read somewhere that there could be some chemical in the water that they don't like and that a carbon filter could help. The LFS wasn't open so I got some black coals out of the fireplace, put them in one of those mesh tomato bags, shook out the fine dust, and put the assembly into the hang-on-back filter. 12 hours later the snails were moving around, and now a week later they are happy as can be eating the diatoms off the rocks.