I have been using Jack's Magic "The Purple Stuff" for some months now, some weeks ago the Phosphate reading was over 18,000 ppm.
This has not been a problem as the pool FC reads from 5.0 to 6.0 (normally closer to 5.0 ppm) with a CYA between 70 and 80. The pool looks very clean with virtually no visible iron stains. This is a first as I now maintain a level of 25 to 30 ppm of Jack's "The Purple Stuff". Prior to this I use to maintain about 14 ppm and slowly but surely the stains returned, this is not the case at this higher maintenance level.
I do cover the pool nightly as trade winds blowing anywhere from 16 mph to 38+ mph across the pool can cause up to a 6 F to 8 F drop in temperature overnight. I have read this can also cause staining due to swings in temperature, I think the nightly covering has helped with the stains.
My only concern is that at some point far into the future, I hope, I will need once again to do an AA treatment. If possible without draining the pool but if necessary it can be drained as it is not a large pool being 10,000 gallons. If the FC is dropped to 0 prior to adding the AA at nightime, and utilizing 32 oz of Algaecide the day before but compensating with enough chlorine to bring it back up to 4 ppm on that prior day, will I have an issue with Ammonia when I add back liquid chlorine in the pre-dawn hours. The reason I mention this is that even at the last no-drain AA treatment it took far more Chlorine than it should have based on a lower Phosphate level of say 4,000 ppm. The expected Phosphate levels might exceed 40,000 ppm or even 80,000 ppm in the future.
Are my concerns unfounded or for safety's sake should I just drain the pool? I realize that this question is more targeted to those of you that have a knowledge of chemistry and how these numbers might affect the outcome, so I hope you see the dilemma.