Thanks. 640w really isn't that much for a 180 as James said. This tank was set up with soft corals in mind and a tight lighting budget. One reason is that I only visit this tank every two weeks, so I didn't think it would be a good idea to have anything in there that wasn't pretty hardy or anything that would use a lot of calcium...just can't depend on folks to keep those levels up. The way the tank is set up now, I do a 30-40 gallon water change twice a month and all the levels stay pretty steady. If I had a bunch of SPS
in there, I expect the calcium levels would be close to nothing by the time I got there to do maintenance. If this was an SPS
tank, it would probably have around 1200w of light total.