I've always had trouble with otos and agree with Jen that the trick may be to get them past a certain time period...but that is the trick! My last otos had a very hard trip...the frantic scooping from the store tank and then the bag had a hole in it and when I got home, they actually squirted out into the cold, dark winter street! I managed to find them and get them into the tank, needless to say without gradual acclimization. I still have three after about a month (had two before, so I'm not sure who the survivors are- one is one of the street survivors.)
I have to try giving them zucchini! I never had done that yet, but the algae is getting sparse in my tank. Mine always seem to be hanging out at the far right of the tank, near the filter intake tubes and heater.