I have a moving bed pond filter made out of a 55 gallon drum where the water comes in the top and goes out a side overflow, and I have a box made of lighting diffuser that sits on top of the barrel where the water comes in, and I usually fill it with polyester batting to use for mechanical filtration, but the only thing I don't like about the batting is that it is kind of expensive, and it is not reusable. I have been researching options for a replacement for the batting for when I restart the filter in the spring, and I came across AquaMaxx filter pads that are machine washable, and I like them, but they come in both 50 and 100 micron sizes. I fear that 50 microns might be too fine, but I worry that 100 microns might not be fine enough, since 50 microns is twice as fine as 100 microns. The pump runs at 3500 GPH. Which do you think would be best, the 50 micron or the 100 micron? I'm not sure what the fineness of the batting was, I just got it at Walmart.