new 90 gal

[purpleoctopus]

how high should my (8)bulb t5 ati fixture be off the water on a 90 gal? its about 30in from my sand to the bulbs.

 

[Fudsey]

This from @ATI North America in another post

One trick to determine this is to turn out all the lights in the room making it as dark as possible. Raise the fixture way up and make a note of the light spillage on the floor. Then lower the light until the light is mostly "captured" by the tank. This will give you the maximum height you would want to run your fixture. At this point you can lower it depending on the locations of your corals and how much intensity you are going for. Of course the closer the fixture to the water the more likely it will get more wear and tear from the salt as well as making it more difficult to work in the tank.

Keep in mind a great deal of the light entering the tank reflects off the glass and will help light up the underside of coral colonies. Some LED options in the market direct so much of the light downward they tend to create shadows since you aren't getting the reflected light off the glass.

But a PAR meter would really be needed to get actual numbers.