Dan,
Your ideas are brilliant. The reason I thought you might have had the CYA tested at the pool store is that you quoted a CYA of 32. That's pretty good discerning on the test since it's hard to know exactly when that black dot disappears. Usually people say something like 30-40 or 35 or something like that.
As for preparing the sample, just take an eyedropper (or a small spoon) and place one drop of water that has visible algae in it onto a slide and then put the slide protector (small square glass piece) over it. The water will spread out evenly under the slide protector. Then you just put that under the microscope and look. You can easily search the net for pictures of pollen. They look like round balls, sometimes with spikes or rough surfaces. and are not very transparent. You can also look for algae cells on the net, though you'll mostly find green algae, but the mustard/yellow stuff will look similar except for color and will look more like cells -- not so spherical, and will have distinguishable features in it -- green chlorophyll in some places but not throughout the cell. The algae should be far more transparent than the pollen.
I must say again, that bucket idea is brilliant. Reminds me of the idea someone had of using a bucket of water outside the pool to see if the pool had a leak. Evaporation would lower the level in the bucket the same as the pool (roughly -- assuming similar water height and wind/sun access) so if the pool had a bigger drop in level than the bucket, then a leak was likely. One could also check levels overnight, but for a slow leak the bucket idea was great.