Filter Cake Build Up on DE filter question/observation

[del]

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.

Del

 

[JoyfulNoise]

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.

Del

I have a QuadDE-100 filter and I will occasionally see about 30sec or so of cloudy water from the returns when I fully tear down my filter and recharge it. It's most noticeable in my spa which is a much smaller volume of water. The spa will definitely get cloudy. Full clarity is restored within a few hours as I always let my filter run for 24 hours straight after a recharge.

The main difference might be flow rate related. Your fish tank filter like has a higher linear flow rate of water through it (and a much more porous DE mesh) so it takes a couple of passes before the DE builds up on the membrane. The Quad cartridge membrane is a much finer scale and the DE probably doesn't move as quickly through the filter so I suspect you see it less. Also, as I eluded too above, my smaller spa looks much cloudier than the pool (you can hardly notice anything in the pool unless it's super bright and sunny out), so you may just not be seeing it.

 

[del]

Thanks for your observations. I will try to somehow circulate spa water next time, but I do not have a skimmer there. I do have a spillway, so I may still be able to use the skimmer.