I have 3 ottos in my 72 gal and I am not sure if I need more of them or the ones that I have are lazy.:;dk I have diatoms everywhere and it does not seem like they are doing anything about it. I feed algae wafers to the tank but I dont think they get a look in as my other tank mates are pretty greedy. I also feed cucumber 1-2 times a week. Is 3 maybe not enough to get the job done?????