Excellent, thank you for the advice. The water chemistry was a little intimidating to start with, but once I'd worked it out it wasn't so bad. I feel much better knowing I can actually measure these things, rather than just blindly throwing chemicals at it. One question before the fun starts - when you say "while the pump is running", do you mean running through the filter, or recirculating? I would guess running through the filter.

The problem with that is the rate at which the filter clogs completely. I've been adding one scoop (as opposed to the recommended-by-the-pool-guy 2-3) DE to the skimmer after any backwash to try to keep the water flowing a little longer. 2-3 scoops sends the pressure shooting quickly up to 20psi above the level it sits at without DE, at which point there seems to be no perceptible flow of water into the skimmers or out of the jets. It'll go +10psi in a matter of ten to fifteen minutes, at which point there is still some very weak flow, but it'll hit +20psi within half an hour, at which point the water doesn't appear to be moving at all. I can keep on top of that over a weekend, but work gets in the way during the week. Do I need to keep the water moving through the filter for the above to do what it needs to do, or will recirculating (or even stagnation) still do the trick?

M