CPE has phosphate remover in it. FWIW, I run Purigen and CPE in my nano. Its a very popular combo for the nano crowd. I have on occasion added a little bit of Rowaphos with the CPE to up the phos removing ability, but not sure if its even needed. I have some extra media bags, and add about 1/3 Cup CPE and 1 Tb Rowa, but my tank is half the size of yours. I change this out every couple of months, or more if I'm lazy, LOL! Are you having any issues now that you think you'd want to add this stuff? Are you skimming?