Have you cycled this tank? Are you aware of the nitrogen cycle?
Otos are very sensitive and because you have such a small tank, and no algae, they may starve to death. You need to see if they will accept algae wafers as a supplement. Some do, some don't and they die.
75: blood parrots, featherfin cat, emperor tetras, turquoise rainbowfish, BN plecos, japanese trapdoor; 46: WCMM, gold inca snails, ghost, bamboo & amano shrimp, kuhli loaches, rummynose & ember tetras, endlers, platies, flame gourami, guppies; 16: pygmy, peppered, loxozonus corys, otos, assassins, RCS ... ~ Research PRIOR to purchase.... ~