Well i have a 10 gallon tank that im working with right now..and i went to petsmart and bought 2 otos about 2 or 3 weeks back, and 2 days later one died of unknown causes. But the other one seems to be living happily in the tank, he is well fed and has perfect coloring, i've read they are happier in schools but should i be concerned about buying another one? He is definitely doing his job ad my algae is slowly being eaten off, should i go back and pick up more? And if so how many should i put in my 10 gallon?
I would follow quarantine procedures for any new fish stock, *especially* purchased from one of the big chain LFS's. Remember, all their tanks are connected (or at least many tanks on a single water circuit), so if a single fish has a disease, there's a fair likelihood of any of their other stock catching it.
That having been said, if you manage to keep an oto alive past a couple weeks, it'll probably live a good long while.