Regarding otos attacking/killing fish, I think it's a response to starvation.
Also it might be particular to some species, or some specimens - I'm convinced my "O. macrospilus" attacked and killed lots of fish for me, whereas my O. vittatus and O. flexilis never have. On the other hand, I've made sure they never starved, like the macrospilus did (I, then, thought they would be able to compete with siamese algae eaters for leftover food & algae pellets. They can't.).
I wrote about it here, also some links:
http://www.forum.planetcatfish.com/view ... ght=attack
Personally I'd remove or destroy any otocinclus which was known to attack fish. I doubt they'll stop, even if nutrition is improved. Certainly my didn't.