get a taller tank for the normal seahorses(kuda,erectus,etc)...its recommended to get 3x their full height....as for smaller thanks you can get into 5 gallons etc with dwarf seahorses but they are a more difficult horse as they require live food 2-3 per day...i have them and they are a handful thats for sure...not hard if you have time for them, but if youre running around it gets tedious feeding.