Time for a SLAM?

[mlawrence17]

I've got a plaster pool and about a month ago I noticed little black spots popping up in the deep end. Lightning had tripped the SWG breaker and so FC was down to 0. I brought it back up to 4 and took a stainless steel brush to the spots. But slowly over the course of a week or two the spots started to come back.

The water is clear, Overnight FC loss test is just under 1.0 ppm, and the CC is .2 so how could algae be growing?
Here are my test results?

FC - 3
ph - 7.9
TA - 90
CH - 300
CYA - 80

 

[jblizzle]

If you see algae, then you need to SLAM. And while at SLAM level, you need to brush the spots to remove the protective layer to allow the chlorine to do its work.

 

[linen]

When you are doing the OCLT, is the swg off?

Also, for 80 ppm cya, you do not want your FC below 4 ppm (ever).

If you smear the black spots, are they green inside?

I would follow jbliz advice and start the SLAM process and do another OCLT tonight to see what it shows at a higher FC level.