[KathyC]

Quote: Originally Posted by boardryder So I thought this would be a great idea to do and did some quick research that everyone might enjoy. I was worried about the plastic under metal halides, but you might worry about your inhabitants before worrying about the plastic if that were the case. At worst it will expand and become a little loose. I believe the pond netting is polypropylene. http://www.polymerprocessing.com/polymers/PP.htmlhttp://www.polymerprocessing.com/polymers/PE.html http://www.dynalabcorp.com/technical_info_nylon.asp Anyway, how is this top doing for everyone? Is it worth doing myself? Is the stuff everyone is using water pond and garden netting? Thanks.

Yes, the netting is polypropylene and it is UV protected and doesn't get brittle under MH's or the sun for that matter Locally it is available at Ace Hardware stores in the Pond Supplies section. The most important point is buying the 3/8" mesh size. With the larger size (1/2") the fish can jump though the openings.
The acrylic that I have been using doesn't expand under the MH lighting at all. The only issue is with slight warping due to trying to span long distances ..in this case a long distance can be 24"... I could not get anyone to cut the acrylic smaller than 3/4" in width due to the danger of cutting it so thin. I'm certain the covers woild not bend at all had I designed them to rest on the upper rim of the tank rather than the inside lip of each opening, but the idea what to keep them flush with the top to be more visually pleasing. A thicker acrylic sandwiching of the netting might make a stronger (no warping) cover also. I am considering trying this with the remaining acrylic I have available.
The cover on my 20" X 18" cube has shown no warpage at all, but again, the distance is smaller.
In all ,the covers have been a great asset and saved the lives of many a fish to date

I do have a newly designed cover but have not posted any pics yet as this one is easier to make, will not warp, will easily fit almost any tank and does not need to be custom made for each application... and I'm going after a patent on this one