Hungry Oto

[bouv2]

I am moving my fish (took over someone else's tank) from a 5 gallon tank to a newly cycled, planted 20 gallon tank. The small tank still has the oto and 5 neons. Although I put a planted piece of driftwood in the new tank, I am concerned the oto won't have enough to eat. I want to get 2 or 3 more otos but want the conditions to be right first. The existing oto will not eat algae wafers (tried 3 kinds), cucumbers, zuchinni or spinach although I've tried everything I can think of. How will I know when the new tank has enough to feed him on, presently there is no visible algae.