Otos "expect" to eat algae in their habitats, and they are very thorough on eating common green algae and diatoms (they will not touoch "problem" algae like black brush, etc). Being ravenous, they can quickly eliminate much of the natural algae, and not being stupid they will find any prepared foods we add for other fish. We hope this occurs; sometimes if the natural algae is too scarce they do not adapt very well to prepared foods and can starve. So seeing yours go after the [prepared food is a good sign.
This is where the prepared food type comes in. Otos are herbivorous so they need algae/spirulina/veggie type foods. Looking up the ingredients in Hikari Micro PelletsI found this:
Fish meal, krill meal, soybean meal, flaked corn, cuttlefish meal, brewers dried yeast, wheat germ meal, wheat starch, fish oil, powdered cellulose, hydrolyzed vegetable sucrose polyesters, dried seaweed meal, lecithin, DL-methionine, garlic, spirulina, astaxanthin, choline chloride, vitamin E supplement, L-ascorbyl-2-polyphosphate (stabilized vitamin C), inositol, d-calcium pantothenate, riboflavin, vitamin A supplement, thiamine mononitrate, pyridoxine hydrochloride, niacin, folic acid, vitamin D3 supplement, biotin, vitamin B12 supplement, P-aminobenzoic acid, disodium phosphate, salt, ferrous sulfate, magnesium sulfate, zinc sulfate, manganese sulfate, copper sulfate, calcium iodate, red 3, yellow 5 (artificial colors).
Two things stand out: the minimal amount of the essential "green" food, and the inappropriateness of using this food for frankly any fish. All that "meal" is junk food and some of it is very hard for fish to digest. I would get a small can of Omega One Veggie Disks. It has no "meals" and is made with fresh kelp/algae and whole fish. My otos thrived on this food.