I have a 15 gallon tank with 1 spaghetti eel, 3 danios, 1 tetra, and two anglefish. One of the anglefish died last night, and the other died this morning. I took a sample of the water to the nearest petsmart and they said it had an ammonia level of 1.2 when it should be 0.0-0.25, a nitrite level...