I wouldn't keep them alone they really like their company and are more out going when there's a few. How many depends on the size of your tank and your stock.
55 gallon elephant nose tank.
30 gallon boraras ,bamboo shrimp, crs,rcs and different snails.
70 gallon elephant nose tank, Gonzo the elephant nose and friends!
30gallon borara merah and brigittae green, red longfin bristlenose, shrimp, ninja, taiwan,bamboo, and snails.