petco has a 14 day guaruntee but they require a water sample for testing. Since it is a new tank that has had fish in it for about a week, the ammonia may test high since it is still going through its cyle period. If water parameters are not good, they may refuse to sell you fish. However, you will want to stick with good strong hardy fish till the cycle is complete. Danios, white clouds and cory catfish work wonderfully and will get along with the gourami. Its always good to have a pair of corys in the tank anyways, they are constantly searching for uneaten food in the gravel.