I think you'd do fine with one pendant, 250 or so. I have only one 400W over my tank AND I have a foot print that's 48" by 36". I'd like to quote Karin for anyone who thinks that's not enough... "I welcome you over to scrape the coraline growth off the class" Todd talked me into just one, and I use the lumenarc reflector. About 15" over the top of the tank.