CH levels, pitting and black spots


LifeTime Supporter
Jul 12, 2011
New Orleans, LA
First let me start by saying that I inherited this pool and most, if not all of the pitting was there when I got it. But it could have gotten worse in the last couple years.

I have some pitting and some etching going on and now they appear to have a black color to them. I assume this is residual algae but I'm not sure. (I had the current limiter recently quit on my SWG)

What causes this pitting and can anything be done to repair it in the short run? (Absent a plaster job) I think my CH is fairly low, but was at a good level last year. I'm in search of the right thing to add, from the right place.

Is the black stuff algae? And how can I get rid of it? I've tried scrubbing and pressurized water. It helps a little, but not much.

FC 5
CC 0.5
PH 7.6
TA 110
CYA 40
CH 170
NaCl 3000

I know my CYA is a little low and my TA is a little high, I'm working on getting those in check now. All advice is appreciated!


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
There are different kinds of pitting. The most common kind is from some combination of low PH, TA, and CH levels, where calcium is leached out of the surface and into the water. You can also get small pits from imperfections in the plaster.


LifeTime Supporter
Jul 12, 2011
New Orleans, LA
Is there anything I can do about it? What about the black spots? Here are some closer pictures

Side wall


The majority of this occurs in the shallowest area of the pool and steps


TFP Expert
LifeTime Supporter
In The Industry
Jul 25, 2011
If the black spots are black algae, try sprinkling some granular chlorine on the spots, either Cal hypo or Dichlor granular.


Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
Tucson, AZ
Try scrapping some of the black off with a fingernail and smear it on a piece of paper. It would look green on the paper if it is algae.


TFP Expert
LifeTime Supporter
May 30, 2007
South Carolina
You need to scrub the algae w/an algae brush. If it is black algae (looks like it to me) the algae brush is needed to knock off the heads of the algae so the chlorine can get inside for the kill. Scrub it before you add chlorine.

Be sure to keep up with which chlorine you are using and how much of what (besides chlorine) you are adding to your pool. You can use the CalHypo until you get the CH in line, then switch to bleach/liquid chlorine. You can also spot- scrub smallish spots with a trichlor tab alternating with algae brush.

You will need to follow the SLAM black algae process with elevated FC levels. See article in Pool School.

Also, for regular brushing for you pool, I suggest a combo brush.