GET THE GLASS UP OFF THE TOP OF YOUR TANK!!!!THE WHOLE POINT OF HAVING METAL HALIDES IS THAT THEY OFFER A HIGHER SPECTRUM OF LIGHT. THE GLASS IN THE WAY ACTUALLY ACTS AS A FILTER FOR MUCH OF THE WAVELENGTH. I CAN TELL YOU FROM EXPERIENCE THAT YOUR TANK CONDITIONS WILL ONLY IMPROVE BY TAKING THE GLASS OFF THE TOP AS YOU'LL HAVE A GREATER AMOUNT OF EVAPORATION AND THE HEAT WILL HAVE AN OPPORTUNITY TO DISIPATE. 5-9 INCHES SHOULD BE A GOOD HEIGHT ABOVE THE WATER TO POSITION YOUR LIGHTS, JUST WATCH THE CORALS THOUGH, THEY'LL BE YOUR BEST GAUGE. IF WATER TEMPERATURE BECOMES A PROBLEM, JUST POSTION ANY HOUSEHOLD FAN TO CIRCULATE AIR ACROSS THE WATER SURFACE. IF YOU HAVE ANY QUESTIONS, I'D BE MORE THAN HAPPY TO HELP
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