I just thought that I would share my observations with my sps growth in my tank. I have always had lower ph levels in my tank with a daytime high of only at best of 8.0 and nightime levels of 7.8 I have had frags that just never seemed to grow. They would always have good color but just no growth. Some went a year with just maybe alittle bit of encrustation. This past summer I discovered that high co2 levels in my basement has been my cause of low ph for all this time. I installed a radon style of fan that I run during the night time hours. Now my ph is usually 8.38 during the day with lights on and a low of 8.1 at night. I have to say that my growth has really taken off with the higher ph. Corals that havent grown in a year are now sending up new growth all over them. I would have never thought that it would make that big of a difference but it sure has. If your fighting little to no growth take a look at your ph levels.
Jeff