Filter sock... Yes or no?

[PFoster]

I use the 7" felt and change them every couple days.
On our fish system we change them every day due to the heavy feedings.

My feeling is that they catch large particulate matter and allow me to remove it before it breaks down or accumulates in the sump.

I feel felt catches more that mesh, but it is definitely hard to get them clean.
We run ours threw the wash 3-4 times in a row and they never go back to 100 % clean but close enough as far as I am concerned. I used to wash them once, then turn them inside out and wash them again. I did find they got cleaner but they also seemed to wear out faster. Now I just wash them a few times in a row without inverting them.