How do snails, frogs, shrimp, and other non-fish-aquatic-animals (nfaa) figure into the 1" per gallon guideline? I was thinking of adding some snails for algae suppression. I see some of those big apple snails and some much smaller snails that have the same-shaped shell. I'm familiar with the small ramshorn snails that multiply a lot. What are these dime-sized, non-ramshorn snails.