After my fourth iron treatment, which requires running at a low FC level, my worst fear was realized - my pool developed some pink mold, even though I had plenty of Polyquat 60 in the water at the time. The pool was never completely without sanitizer, but I have a very high CYA (my plan all along was to do a partial dump at the end of the season to correct this), so I guess running below 3 ppm for several days, even with algaecide, caused the problem.
The first thing I did was brush off all visible pink mold (I know this is actually bacteria and not algae). It appeared on my steps and around the light fixture, also in the skimmer and beneath the bottom ladder rung (didn't catch the ladder issue right away). Then I shocked, vacuumed, backwashed, and am continuing to shock and brush.
With a CYA somewhere between 80 to 100 (I have a hard time doing this test and seeing when the black dot disappears), my shock level is probably in the low 30s. I have been trying to maintain this level, but it's been difficult because of work, and when I come home, the FC level is back in the teens by late afternoon.
So I'm off work today and am maintaining a level of 35. Seems to be holding right now. I have not seen any actual pink in over 24 hours. However, there is one spot along the liner seam, on the pool floor in the shallow end, where a white film or powder keeps appearing. Even at FC 35 ppm. I have to keep brushing it off. The first time I saw it a few days ago, I thought it was DE powder, but on close inspection, it seems more gel like. Also, the first time I saw it, there was some pink attached to it, so I assume this is either biofilm or white mold - I don't know if there is a difference. Now the white stuff keeps coming back with no pink on it and it brushes away and turns to dust. It is about 4 or five inches wide and maybe 15 inches long. Does anyone know what this is or why it keeps coming back to the same place, within hours after being brushed up? There is also some powder like substance appearing nearby all along the seem of the liner. Again, this brushes up easily like dust. Also, when I brush the liner, this seems to create dust clouds even in places where I don't see anything at all. Like there is invisible dust or powder everywhere.
Is it possible this could be DE powder? A few years ago when one of my filter grids had to be replaced, the powder appeared in the seams like this. I have been putting the poor filter through **** this season - lots of backwashing between metal treatments.
CC 0 to .5
CYA 80 to 100 ?