Has this tank cycled yet? I don't think you've had enough time to cycle the tank. Please take the fish back and properly cycle your tank....
How to cycle your tank with out the use of fish
How many pounds of LR
do you have in the tank now?
What other filtration are you running?
Did you every buy the test kits?
If so, what are your current water parameters?
Did you see and ammonia spike and fall followed by a nitrite spike and fall followed by a nitrate spike?
Did you then do a large (30% - 50%) water change?
If I'm off base here, I apologize. If not, please don't kill that fish by keeping it in the uncycled tank.