I wouldn't permenantly keep them in anything smaller than a five gallon. I sometimes move one of my otos over to my kids five gallon betta tank when it needs alittle clean up. He seems to do fine in there. If you have a bigger tank, maybe you could keep them there and just drop one a couple days to eat up the algae. You could try some snails, my cocrkoaches seem to keep the glass clean of anything but green spot.