I'm saying that so you are prepared for it to happen, which I'm almost certain it will. From what I'm reading, you don't have any live rock right? And there is no other filtration on the tank, just an U/G and powerheads? If that is the case then it will re-cycle because there is no other means of biological support. If you can add LS and LR (cured) and the nitrifying bacteria in a can (comes in a red film case looking pack, don't know the name brand though). This will minimize cycle and could eliminate it completely. Buy a large rubbermaid or Sterilite container and put the fish in there with the powerhaeds and heater. Put enough sand and LS to make a 4-5" sand bed. This will have to settle for a day or two for the water to clear. Then add LR (if your going to add any) and carefully put back the rest of the water and fish. Keep a good eye on the water parameters and have water available to make water changes in case of a cycle. Test kits will be a must. Good luck.
