After going back and forth countless times the past few weeks over whether I have mustard algae or pollen/dust that continually shows up all over the bottom of my pool as soon as a day after vacuuming, I decided to go through the shock process as if I do have mustard algae. I want to post my experience to make sure I am doing things right.
First I vacuumed the pool bottom clean yesterday morning and then added enough bleach to get to 25ppm(cya is 40). Yesterday was raining off and on all day but never a heavy downpour. Tested about an hour after adding and got a reading of 20ppm so I added enough to get back to around 25-26 and let it go till right before dark. Tested again(right before dark) and showed 20 again(maybe this bleach isnt as potent as I thought) so I added enough again to get to 25 and called it a night. This am I tested and have 21 maybe 22(doesnt look like it rained last night much at all)
The thing that baffles me is that the brown spots that have plagued me have reappeared in the bottom at different parts of the pool from yesterday afternoon to this a.m. Am I at a high enough level to come to the conclusion that this is dust/pollen and NOT mustard? I thought I read somewhere that mustard would not reappear while you are at a shock level? Or is this just a nasty case of mustard that isn't going away this easily? I might add that there is nothing growing on the wallls and never has been.
Should I continue to keep the pool at a level of 25ppm even in the day?(today is sunny and the rain looks to be gone)