Looking for help/advice.
Heavy green algae burden, trying to reclaim the pool now. I did BBB last season, successfully, but lazily let it get out of hand this spring. It's swamp green.
CYA zero (!) - this surprised me as it was around 40 all last season
I had 5 lbs of dichlor on hand, so added that (should bring CYA up to 12), and brought FC the rest of the way up to shock level with bleach, and have kept it up as per SLAM. I put another 2 lbs CYA in a sock in the skimmer. I put another 2 lbs CYA per the instructions on the bag (mix in bucket of warm water, pour slowly into skimmer). Not sure that was a good idea, but my thoughts were that it's how the manufacturer recommends adding it, and wanted to get the level up sooner than later. If and when all that CYA dissolves, it should bring it up to about 30.
Here's my dilemma. The algae burden is so great that the filter grids (Pentair FNS Plus, 36, DE) clog incredibly fast. Backwash on my system has never worked well, I always remove and hose down the grids. It's impractical (though I may need to) wash them every few hours. So, I decided to just run the filter without the grids, figuring I'd just do the continuous chlorine shock to kill the algae, then deal with the grids and get rid of all the dead biomass after a few days. My other thought was that since I just added all the CYA, changing DE and washing grids every few hours would remove most or all of the not-yet-dissolved CYA. Does this make sense?
After 36 hours of keeping the FC at or near shock level, the algae looks just as dark green as when I started. I would have expected it to lighten, to cloudy grey, or at least look like there's some progress. Shock level is 10 per poolcalculator, I've aimed for 12. Lowest it's been during SLAM (morning) was 6. Is there any benefit to shocking to a higher level? Even using the expected eventual CYA level of 30, shock level would be 12, which I've been doing. I did remeasure CYA, and it was up to about 15 (gross estimate, half-way between the 20 and the top of the cylinder in the TFT kit).
Summary major questions:
1) Leave filter grids out for now or run with them in and risk losing CYA?
2) Any benefit to higher-than-calculated shocking?
3) Should I have seen some progress in killing algae by now?
25,000 gal, plaster
Pentair FNS Plus 36, DE filter
3/4 HP Whisperflow pump
BBB believer, trying to be disciplined enough to make it work!