I have an issue that I would like some additional expertise on. I battled this same issue last year as well. To make a long story short, I have had some fine, brownish-green (mostly brown) "stuff" in the the cracks and wrinkles of my pool all summer. It poofs up and disperses into the water when brushed and makes the water cloudy in that local area. I continue to brush and then vacuum this "stuff" to waste. I maintain FC levels using liquid bleach (8.25%) according to the FC/CYA chart from this website. I have always struggled with really knowing if this "stuff" was algae or not. Last week, I had a definite algae issue. I could not see the bottom of the deep end (7ft). I SLAM'ed according to this site, brushed everyday, and vacuumed the piles of dead "stuff" to waste each day. It took about four days and 8-10 gallons of bleach until I got clear water, 0 FC loss overnight, and 0 CC. I thought I was done.
After the SLAM'ing, I noticed the same "stuff" appear the very next day. The "stuff" does not appear until after I turn the pump on and let it run a few hours. Then I see the "stuff" reappearing on the bottom of the pool. I was confident it was very fine debris coming from the filter (no pollen in the area and just SLAM'ed). And then today I get home from work and the bottom has a slight layer of "stuff" once again. I brush the "stuff" and there is a poof of light green on each brush stroke.
The part I can't understand is I have not let the FC drop below or even to the minimum of the FC/CYA chart. I checked the FC last night and again this morning (four days after the SLAM) and had zero FC loss overnight. The value was 4.5 ppm and 7.5 pH during the OCLT. (I have been checking the FC each night trying to determine if I have organics or not.)
Is it possible algae is being introduced to the pool from the filter? Any other ideas? At times, I have not ran the pump to see what happens. When the pump doesn't run, this "stuff" does not appear in the cracks and wrinkles. When I turn the pump for a few hours, the "stuff" is back and continues to accumulate as long as the pump is running
Pool chemical readings:
FC - 4.5
CC - 0.0
pH - 7.5
CYA - 30
CH - 350
TA - 90
Thank you for the support. This site is awesome and extremely helpful.