DIY Tank covers that don't cut out light?

[asylumdown]

I've read a bunch of forums looking for suggestions on tank covers and I'm wondering if anyone has a novel idea I haven't heard of yet. I have 2x250 watts of 10 000k metal halide and 250watts of actinic lighting in a fixture that sits on top of the tank with maybe 5-6 inches of clearance to the surface of the water. The very first wrasse I ever got lasted all of a day before it launched itself to it's doom while I was at work so I built a nylon cover netting cover. My second wrasse, a lineatus, managed to sail through it as though it wasn't even there (he was either very strong or very unlucky) when I was in Palm Springs. I then replaced him with mystery wrasse, which had tail and fin rot. I spent over a week putting hours of daily effort in to that guy getting him well in a hospital tank and 2 days ago he went in to the display. This time, I used white egg crate to make a firmly fitted cover for the whole tank with holes for equipment cut to exactly snug dimensions. Leave it to my luck to have him leap out unnoticed as I was doing a full clean of the glass and water change and not notice as he died on the floor 2 feet from me. You could still see the wet marks where he had bounced around on the floor when I noticed him.

That. Truly. Sucked.

Anyway, I have noticed a visible difference in the amount of light hitting the sand with the cover and without. it's most noticeable in the corners of the tank as the MH bulbs are relatively centred in the fixture. I have a soft spot for wrasses - they are by far my favourite fish and I would very much like to replace either my fairy or lineatus wrasse but I don't want to compromise the light getting to my corals (I have tons of sps that have been doing incredibly well, I'm afraid to change that). Does anyone have a novel solution that can be made to fit without either cooking my tank, looking terrible or dramatically impacting the light?