Algae behind plaster

[Beachkimball]

Hi all,

I've had my house/pool a little over a year, and this morning as I was brushing the walls, I noticed some dark green spots. Investigating, I see that they are actually behind the plaster. As I peeled off a little off the plaster just with my fingernail (you can see in the second pic where I peeled off a little dime sized piece of plaster, I found more green behind it. When I rub the spots with my finger, a familiar green cloudiness rubs off into the water.

My questions are:
1. It's not staining through the walls at all, and all my levels are good, but can algae live behind the plaster where the chlorine doesn't affect it, and not show through the walls?
2. What do I do about it? I just finished my last SLAM like 3 weeks ago. Do I need to SLAM again, even though the water is crystal clear and all tests are good? I'm worried that the SLAM will kill what's visible, but then there will be more underneath anyway. I brush the pool every few days like clockwork, and just noticed this the last few days.

Thanks for any help. Pics attached. Test results are shared through the app, but just in case, posted below.

Brett

FC 8.5 (like I said, I'm very very slowly and cautiously allowing myself to let them fall - I have had algae blooms every few months or so since I moved it, and the last algae bloom I had was in early May, when my pH was at like 7.8, CYA was 80-90, and FC never dropped below 7.5. So I'm very carefully and slowly bringing the FC back into range).
CC 0
pH 7.7
TA 80
CH 300
CYA 70
Temp: 80 degrees

 

[ajw22]

You have old delaminating plaster where water and algae can get behind.

Algae has a biofilm that protects it from chlorine attacking it. Brushing the walls breaks up the biofilm to allow chlorine to do its job. You cannot get to the algae hiding behind the plaster to break up the biofilm. It is going to be difficult to rid your pool of the hidden algae depending on how widespread your plaster problems are. That is why you keep on getting algae outbreaks.

The long term solution is a replaster job.

 

[Beachkimball]

Thank you! I’ll plan to do that in the fall I guess. In the short term, am I doing the right thing just keeping the FC a little higher than I should, brushing, and watching the walls for spots and then attacking those vigorously? Or is that just wasting my time, and I should just accept that I’m going to have regular algae outbreaks until I replaster?

 

[ajw22]

Thank you! I’ll plan to do that in the fall I guess. In the short term, am I doing the right thing just keeping the FC a little higher than I should, brushing, and watching the walls for spots and then attacking those vigorously? Or is that just wasting my time, and I should just accept that I’m going to have regular algae outbreaks until I replaster?

That is the best you can do to try and sty ahead of any big algae replication.

Understand that what to ther folks may just be a small dip in the FC target and not cause an algae outbreak, with algae lurking in yous water any dip below the target FC level will likley give the algae an opportunity to grow quickly. And you will have a higher daily FC consumption then an algae free pool.

So keep your FC on the high end and don't let it drop.