metal halide height

[adamRS80]

I've set up a little frag tank and I'm not sure what the best height would be for the MH fixture above the tank. The tank is only 16" deep and the light is a 250w Aqualine 10k. How high should I place the light? I'll be keeping mainly SPS, and clams in this tank. Thanks for the advice.

[Tim Marvin]

If it has a shield and it isn't being splashed, put it as close as you can with it still lighting the whole tank. Also remember you may want to put your hands in there to frag stuff so make it easy to get by or move out of the way.

[adamRS80]

Thanks Tim. Right now I have it about 6" above the water surface. I had it about 3" from the surface and two of my montipora frags started losing their color so I figured it was a little too close. One other question. Do you think it would be ok to use acrylic as a cover for the tank? I have some extra 1/8" lying around and I'd like to cut down on evaporation. Does acrylic block light worse than glass? Thanks again.

[dan]

i think it is worse because the acrylic will bead the light rays coming it the tank. the acrylic will also bead being on top of the water.

[PeeJ]

dan could you explain bead?

[matt]

Acrylic has beter light transmission than glass, but if it gets hot enough under the light it will melt. It won't take long if the light is really close. You'll also get some pretty quick heat build up under the top as well; greenhouse style. I don't know what Dan means by bead either.

[MikeP]

going to take a wild guess and say Dan probably meant to say 'bend'.

[PeeJ]

thats what i thought too

[dan]

sorry about that :oops: ya 'bend'

[adamRS80]

So is it bad if it bends the light? My sump will still be open so I don't think heat will be too much of an issue. Matt you said it has better light penetration than glass, dan have you had a different experience? I don't think it'll be close enough to melt it. I just want to minimize the loss of light intensity but I do need some sort of cover. Thanks guys.

[Tim Marvin]

1/8 inch will warp for sure.

[Instar]

Acrylic will block (filter might be a better word) from 9% to 11% of the light, mostly in the ultraviolet range, but, only these percentages.
Glass will block from 30 something (possibly a bit less with an optically clear perfect glass - expensive) to nearly 50 something depending on tint and thickness.