This question has no real practical use, but I will ask it anyway. I have used small DE filters for fish tanks, and it is necessary to recirculate the water in the filter a few times to build up the "filter cake" before the water becomes clear. This seems reasonable to me, as the filter mesh has fairly large openings and the DE particles need a chance to stick together to be able to filter all of the DE particles, which then become the "cake" prior to the filter actually being used as a filter. For my pool, I have a Pentair Quad 4 60 sq. ft. DE filter. Yesterday, I cleaned the four cartridges thoroughly, and then introduced 6 pounds of new DE to the cleaned filter via the skimmer. During the addition process there was no sign of any DE coming back into the pool at any point (which is just great!), even when it was doubtful that a filter cake existed on the DE filter cartridge membranes. My question is why is this the case? Why doesn't it take a few hours to catch all of the DE on the filter cloth/membrane? I can see that this may be the case if the membranes have truly small pores sizes to them, but by looking at them, this does not seem to be the case. Again, this is just a curiosity post and might be a bit of fun to discuss.