I have 2 Ocean Revive D120 lights and was wondering how high they should be. My tank is a deep blue 80 frag tank. Would 6 inches off the water be good or do they need to be higher or lower? There will be SPS and LPS in the tank.
Also I have an AISol Super Blue over a 40 breeder with zoas and mushrooms. How high should it be above the water?
How high off the water you set your lights is not just some random number. It depends on several variables: 1. the size of your tank (L x W), 2. how deep your tank is, 3. what light fixture you have, 4. what lenses your light has, 5. what are you trying to grow under the light, and 6. convenience of use for getting in and out of the tank? Before leds had dimmers or controller/timers, how high you set it off the water was a
critical issue to how strong the light was in the water (PAR values). With dimmers, PAR is now much more controllable and how high off the water you set your light is more about good light spread and convenience than PAR values.
You want to set the light just high enough so that the entire tank is lit up, and not much, if any, is spilling outside the tank (which is just wasted light and wasted energy use). If your tank is shallow, like your 16" deep frag tank, you want to set it high enough that you can run the light at 50% power or more (after the corals have been acclimated to it). With a shallow tank if you have a light with 90 degree lenses, you may want to go a bit higher in order to light the entire tank and because the light is being focuses down into the tank more directly to improve how well the light penetrates the water and gives better PAR values at deeper levels (not much of an issue with a 16" deep tank). The best situation would be to set the light so it lights the entire tank and then set the power to give you the PAR level you want (measuring with a PAR meter and not guessing). If you don't have access to a PAR meter, start with low power levels and allow your corals to acclimate as you ramp up the power levels over several weeks.
I hope this helps and feel free to ask questions in our OR sponsor forum here on R2R.
