Dark Spots on Plaster

[Daniel76120]

Hello there,

I was brushing my pool today and noticed that I have little dark spots all over my stairs, I decided to throw some granular chlorine on top of the stains and it did nothing. I went to Leslie’s, to get my pool parameters, and I have little to no copper or metals. I showed the pictures to the employee and they mentioned that it was algae and that I need to shock, so that’s what I’ll be doing tonight. Don’t know if that is going to work. I usually keep my FC around 5-8 due to my CYA so I’m kind of weird out that it is algae.

Any recommendation of what it could be?

FC 6
CC 6.60
TA: 90
PH: 7.4
Hardness: 320
CYA: 58

 

[mknauss]

That is not algae. And a 'shock' does nothing. You follow the SLAM Process for algae.

Have you tried vitamin C tablets in a thin sock, crush them up a bit, and set it on the spots.

 

[Daniel76120]

That is not algae. And a 'shock' does nothing. You follow the SLAM Process for algae.

Have you tried vitamin C tablets in a thin sock, crush them up a bit, and set it on the spots.

Yes, I tried that last week, some spots do look dark orange /red-ish so I thought it was rust or organic material but no change. I let the sock sit on the darkest stain for a few minutes and no change.

 

[mknauss]

OK -- if you take a wooden skewer or toothpick can you get any material out of the spots? If so, wipe it on a paper towel. If green, it is black algae, which is cyanobacteria. You eliminate that differently than algae.

 

[Daniel76120]

OK -- if you take a wooden skewer or toothpick can you get any material out of the spots? If so, wipe it on a paper towel. If green, it is black algae, which is cyanobacteria. You eliminate that differently than algae.

They spread on orange-ish color.

 

[mknauss]

Then they are likely organic if there is a soft material associated with them.

Read Black Algae. I suspect following the protocols in that article will help. But you need to be able to disturb them so the chlorinated water can get to it.