Hey Randy, I almost finished typing my response when I saw yours come through. I had the same thoughts about the window screen.
Hey bobdog,
I think the coated cloth and the chicken wire are good solutions, but I'm not as sure about the window screen. Whatever you use I think it should allow as much direct contact with the filter material as possible.
I have a theory that successful drainage in a BSF unit is achieved through a material that wicks liquids as opposed to the liquid flowing through holes. The BSF residue seems to clog any size or number of holes. But, when the residue directly contacts something like coconut fiber or synthetic air conditioner filter the liquid wicks along the individual fibers.
Window screen might work by also wicking the liquid, but there is another potential problem with it; it could trap larvae beneath it. The larvae will always work their way into the filter material, and they grow so quickly they could possibly get too big to pass back through. To eliminate that possibility you need to use a mesh that will allow a fully grown larvae to pass through.
Anyway, thanks for the input, sooner or later I'll try using one of these materials to sandwich the filter medium.
