Here's a good calculator that I've used a few times. http://www.reefcentral.com/calc/hlc2.php An alternative option is placing the sump above the tank, the pump is in the tank and pumps up to the sump, the water flows back down from the sump, and no overflows are needed. You'll just need to drill the sump once, an acrylic tank would make it easier also, hmm and leds also. a bookshelf macro reef