I just cleaned my Fluval FX6 after the PH started to rise. The dirtyest part was the very top sponge. I replaced the first filter which was previously UGF gravel with SeaChem's matrix. I know it's supposed to have the most surface of any bio-media but my mind keeps telling me they just look like rocks. Won't the little tubules get clogged eventually? Also I change my filter once a month and it's quite involved. Do you think I could get away with just just rinsing out the top sponge?