[emccullough1]

As for gray pvc you could use electrical conduit but it is more costly. They make a spray paint foe plastic that is safe. I would probably go that way but that is just me. I'm a big deep sand bed fan so something between 3" to 5" would work. But there again that is just me. Whether you would get much help with nitrates from it would be questionable. But LR and LS and some micro algae sure is not going to hurt. I had more room then you and made my refugium 10 gal which is the same as my tank, total 20 gal counting sump And it has maid all the difference in the world. I could not keep my nitrates below 20 and now they run around 5 at the highest.