I have not seen mine taking care of BBA and nothing that I know of eats BGA but the rest of the tank always looks spotless when I have any otos in it. I'm not sure what forms they are eating because I never see it. I will usually add otos when there is a heavy layer of green stuff developing all over the tank but it is usually the kind that is easily removed with a scraper. A week or two later I find I need to supplement the otocinclus no matter how much algae I started with.