I'm confused, do you have a phosphate filter in your system or not? The one I've seen looks like finely crushed brown stones. It's sold as gravel or it comes with a clear canister that attaches to a relatively small pump (sold separately). This help control my brown algae problem as per members recommendations on this forum. However my tank is new and I started early so the issue was caught before it took over. But the rate at which the brown algae was spreading was very fast. The phosphate reactor wasn't expensive really considering it's a German brand (Aqua Medic) and small Chinese pump. The LFS said a strong pump will not allow the water to filter properly and may push gravel out of the canister.
Cheers
Wael