I run both Carbon and Phosphate absorbing media in my reef 24/7 I replace my carbon every two weeks and my Phosphate media once a month. There are different types of Phosphate absorbing media though and I have heard some people having problems with the kind that is made from aluminum(it usually is gray or white in color) I use the ferric based media it looks like rust and is basically rust lol. There are also different types of carbon also, some of the cheaper carbon can actually release phosphates into your water if I remember correctly, depending on what it is made of. Joel would be a good one to get the full story on this pm him or maybe he will notice the post and chime in.