It's not going to kill him to be without a school but he will be unhappy. One you get a bigger tank and get everyone settled in go to a store that can tell you what kind of algae eater they are selling you and get a few buddies for him.
Okay I will definitely do that. So, the question remains. I need 2.5 gallons for my Betta. How much for each oto, each frog, and each snail? So I can figure how I will divide them up later if necessary?
The otos get to be about 1.5 inches so if you follow the 1 gallon per inch of fish that's 7.5 gallons, I'm reading 1 gallon of water per frog so that takes you up to 9.5 so for just the otos,frogs, and snails 10 is ok. If you want the betta in there too you can get rid of the 2.5 and just get a 15-20 gallon and everyone can go in that.