Btw, how are you measuring your salinity? Are you using a swing arm hydrometer or a refractometer? The hydrometers can be very inaccurate, so your salinity could be swinging without you realizing this. If you're going to be keeping sensitive corals like SPS, you should be using a refractometer to measure salinity. You can get a good one off ebay for $30 or less. Also, how are you topping off? As your water evaporates, the salinity will rise, and if this is a big swing, that could stress out the SPS. You should be topping off with fresh (not saltwater) RO/DI water to keep your water level stable. Depending on your evaporation, you may need to do this every day or a couple times per day. If you want to keep your salinity very stable, the best way is to get an auto top off system, which will top off with fresh water automatically as needed.