I just bought my gilfriend her very first aquarium for her birthday. Its your basic 10 gallon kit with everything heater, filter, lights and hood. We filled it with two kissing gouramis and three black skirt tetras and a bunch of plants. We conditioned the water before putting the fish in using water softener. It's been about three days since she has had them and we discovered today that one of the black skirt tetras is dead. We have no clue why and we dont know what to think. Im going to get her a testing kit to see if the ph is too high and check the nitrate/nitrite levels. Any other ideas?