I've never used a wet/dry but am under the impression that they work like a bio-wheel. The provide a place for bacteria to thrive and convert waste to nitrate. I had red algae covering my gravel no matter how much I hoovered it or how much water I changed. I also had a problem with bubbles in my tank from my skimmer and my bio-wheel, so I asked my LFS how I could reduce the amount of bubbles in my tank and he told me to take off the bio-wheel. A week later, I not only had less bubbles in my tank, I also had no algae on my gravel. The bio-wheel was loading down my tank with nitrates, even though my tests were negative, so now I rely on my live rock which takes out all the wastes without producing much nitrate. Not sure if this will help you, but thought I would try. BTW, my 30gal is overstocked with 7 fish and I still don't register any harmful wastes in any test. Live rock is natures way!!
