My frag tank is 6ft long and I have a MH pendent on one side that covers a 2x2 area and a 2x96 PC DIY fixture for the other 4x2 section.
On the chemical warfare issue, I have a little rubbermaid box that the frag tank drains into that I keep a bag of carbon and some sponge in. The water drain from it into the sump via holes I drilled.
Congrats on the frag tank. I started with a 10gal, then I had a 20L, then a 33L and now I have a 72x24x13 frag tank. 
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*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,
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