I have a golden nugget that does'nt seem to be growing at all he seems fine happy and healthy and eats plenty but has not gained any length since i purchased him. He is about 2/3 inches long and was thinking this maybe his supposed size but have read many posts saying that they get alot ...
Off the top of my head your tank with gravel,ornaments ect should be around 40 gallons,Has a general rule of thumb you can have an inch of fish per gallon.
I would go for around 35/36 inches of fish,Of course this does'nt apply to one 36 inch fish!
Oto's love algae wafers and lettuce IMO,All my oto's are well fed and show this,Oto's will spend ages rasping on algae wafers if other fish allow this.