The only two reasons for the CYA discrepancy are 1)incorrect testing, and 2)swampy green water. Severe algae outbreaks do have a tendency to break down the CYA, so if the algae bloom happened in that 2 weeks between 5/27 and 6/5, that could have been the culprit. You can add CYA in your skimmer, or in a sock in front of a return, and give it 1 week or so to dissolve. To clear up your water, you need to dose it with bleach to get it up to 10-12 ppm and keep it there by daily additions until the green is gone and the filter clears the water.

Your most important task, though, is to get the pucks in the floaters out of your pool and raise your pH using Borax before you have damage. 7.0 should be your minimum pH.

Janet