Olive Nerite Snails, but they live in tidal zones so they'll want to stay above the water line a lot of the time. Make sure you have a lid. Only thing is they will reproduce if they're in brackish where they don't in freshwater.
Malyasian Trumpet Snails will work too. They're livebearers that only reproduce one at a time so they'll repreduce much slower. They burrow in the sand so that's a major plus too.
40G Brackish Mangrove Swamp
(4) Toxotes Jaculatrix
(2) Uca Spp.
37G Puffer Tank
(1) Tetraodon nigroviridis
200G Mangrove Swamp (Under Construction)