Ok, with a Tagelus 60D, the absolute do not exceed is 47GPM. Do NOT take that sucker off low speed. You can probably even backwash on low. (Need about 40 GPM for that).

The pressure behavior you're describing is pretty typical of DE; it re-compacts under restored flow.

Also, we've got a rash of problems like yours -- probably because so many pools got 'slimed' during the exceptionally warm spring. The good side of all this (for me) is that it's giving me a widespread pattern to look at. In EVERY case, an over-pressurized sand filter has been involved. However, in one case, we're NOT seeing what we've always presumed; that the particles would be filtered by a DE or cartridge filter. In this case, the owner cleaned up (de-greened) with sand, and then switched to a cartridge, and now STILL cannot filter the cloud.

What I think may be happening is that the high rate / high flow through the sand filter is fracturing the algae particles and they are leaving the sand filter as a stream of much finer particles than when they entered. So, what I'm asking people to try, is to raise the chlorine high enough to last a couple of days, and to then turn the pump off.

My hope is, it will settle some. If it settles enough to vacuum out on waste, then we have a solution. If not, the next step is to try a floc, and then a clarifier. But it appears that these particles may not filter out in any reasonable time, except with an over-sized (low flow per sft) DE filter --- and that would be EXPENSIVE.

The way to avoid it in the future is to NEVER allow algae to be forced through a sand or cartridge filter by an oversized pump.