We're looking to add a third tank, but this time without fish -- just watery critters. Currently there are amano, cherry red, and bumblebee shrimps; nerite, trumpet, and basic pond snails (on purpose!) assorted around in the current two.

Other than various shrimps and snails, the dwarf frogs... is there anything else that could be kept in a non-fishy community? I can't think of anything, and not much comes up in searches, I don't know if I'm using the correct words and/or phrases...

All planted freshwaters, btw. The third tank would likely be 10 gallons, so obviously small species. Unless there is something large out there that my husband couldn't possibly resist -- I'm still pulling for that 75.

Thanks, if you've input. ;)