I have been reading a lot on this site in the last few months and appreciate all the useful information. I have have an issue with a green pool and have also had black algae off and on again for the last few months.
I have through reading this site been able to manage and temporarily get rid of the black algae and it has been basically not existant for about a month now.
I test the water morning and night (no less than once a day) and keep the fc level no lower than 3 ppm. I have a target of 5-7 ppm that I normally keep it at. It never holds chlorine (which my pool service guy says it will eventually) but from reading info here I realize that it is not uncommon for it to lose some due to sunlight. Last week I was adding the lowest amount I have in months and it was only losing approx. 1 to 1 1/2 ppm daily. I thought this was pretty good. My pool service also have been using chlorine tabs in the skimmers and I think that helped to maintain the levels.
As of Friday everything was looking good. Then by Saturday I started to notice a major loss of fc. 4-7 ppm. I raised the fc level to 16 ppm and overnight it lossed 8 ppm? At this point (Saturday) I found a small area that had the black algae appearing, but thought that maybe it had been there the whole time and that I hadn't noticed it.
I shocked it today (Sunday am) and raised it to 16 ppm. By 6 pm it was back down to 8 ppm. I raised it back up to 16 ppm by adding bleach.
By early evening, I started to look closely and everywhere I look the black algae is coming back...
I am wondering how in one day the black algae can start to come back even with the fc levels not falling below 3 ppm?
Should I keep it from going below 5-6 ppm instead?
I am so tired of shocking and not being able to enjoy the pool, and to go through it all again 2-3 weeks later when I think I have it under control-help...
water is still clear and looks good
Current test results:
fc 8 (prior to shocking)
calc. hard. 220
cya 35 (read 40 last week)
Thanks for your time!