[Raul-7]

how many oto in a 10 gal tank?

The genral rule is one per every 10g gallons, some people use more, others use less. But in a 10g, I think one will be the maximum...one thing to remember is that they do better in groups of 3 or more. Maybe you could use shrimp instead?

 

[Raul-7]

They may get darker as they get older, but you have to remember there are numerous species of the genus Otocinclus.