Plaster pitting

Apr 26, 2012
I'm having some pitting problems with my plaster, and the pits are gathering alge.
Trying to figure out why it's pitting like this. Getting worse.

The pool was replastered 5 years ago.

My PH always runs high and I use acid every few days to bring it down.

CH is 200
TA is 80
PH is 7.6 today
Cya 35
FH 3
Water temp 77f

Been using bleach in pool for 5 years and water always looks good but I do get these algae spots in the pits.

Any ideas?


Mod Squad
TFP Expert
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LifeTime Supporter
Aug 10, 2012
The pitting is called etching and results from having low CH causing calcium to dissolve from the plaster into the water. To prevent etching you need to manage your CSI between -0.3 and +0.3. This is done by entering all of your test results in Poolmath and it will calculate your CSI. Adjust CH, TA and PH to get the CSI into range. Your CH needs to be a minimum of 250, 350 if you have saltwater.

More here, Pool School - Recommended Levels
And here, Langelier and Calcite Saturation Indices (LSI and CSI)

Add your location (city and ST) to your profile so it shows up over there <----, climate is important when we are helping you with your pool. Also, add your pool info to your sig so we know what type of pool equipment we are helping you with, more here, Pool School - Read This Before You Post