I use 100 micron bags. I have to hose them off about every 3-4 days. Here is some material about micron ratings from filterbag.com:
Micron Ratings
A micron is one millionth of a meter (0.00003937 inches). By contrast, a human hair is about 100 microns in diameter.
It's important to understand what kind of micron rating you're using when selecting a filter bag. For historical reasons most filter material is assigned a micron rating based on approximately 80% efficiency. Filters that remove 80% of all particles larger than 50 microns in a single pass are rated 50 microns.
Filter bags made out of monofilament mesh or micro-fiber are given absolute ratings. A filter bag with an absolute rating will capture 99% of its rated particles in a single pass.
Filters are sometimes measured in U.S. Wire Mesh instead of microns. Wire mesh measures the number of wires (or threads) per linear inch, not the size of the holes between them. As the number of wires per inch goes up, the size of the holes (in microns) goes down. There is no simple formula to convert between microns and wire mesh because it would have to account for changing wire diameter.
TChristman;601321 wrote: I use felt now but will most likely go with mesh on the new tank. 100 to 200 is fine. I think 100 felt gets clogged much easier than mesh.
I've been wanting to try some 150 micron mesh bags. I keep up with it, but the 100s clog pretty quickly. Sometimes, 200 seems like it doesn't do enough to me.