Welcome to the forum!
Please click this link and read about cycling your tank: http://www.aquariumadvice.com/forums...es-154837.html
It's not as easy as just putting water in a new tank and tossing a fish in. You have to cycle the tank first to be sure the water parameters are safe for the fish.
You may just have a high level of oxygen in your water. It could be a number of things. Please give more information as to whether or not this is a brand new set up, what was put into the tank (chemicals), what instruction you were given by the store, etc.
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.... ~