Plaster disintegration and water chemistry

HGalindo

Member
Apr 16, 2020
11
Dallas, TX
Hi everybody,

Question first: Is there a particular aspect of water chemistry that I should focus on if I want to halt the degradation of my quartz plaster?

Background: Pool is entering its 7th year of life. I noticed late last summer that the pool cleaner bag was containing increasingly larger amounts of plaster particles. Our pool repair person was out to fix a different issue and I brought this up and he suggested we have "harsh" water and that's causing the plaster to degrade. Said to dial the chlorine way back. So I did. And not long after, we covered the pool for the winter and I mostly just ignored it because that's what I do every winter (though we don't always cover it). Enter massive algae bloom stage left.

So, now, here I am getting my pool chemistry degree at the U of TFP and trying to get my chems right. Don't particularly wanting to drain the pool again (ETA: CYA was 190, now down to 80 after draining this weekend and hoping spring rains will replace enough water to get the CYA down eventually). I know the chlorine is safe because the high CYA is buffering it. But my TA is 100, which I know is a bit high, my pH is pretty steadily in the 7.5-7.6 range and my CH is 250. Is there anything about these other numbers that I need to worry about as far as how it affects plaster?

FWIW, there's no pitting, a few hairline cracks because Dallas soil is the freaking worst, but a bucket test says we're not losing water, so the plaster seems okay structurally, but you can wipe your hand across it and remove particles. It's very rough and sandy, especially around the steps.

Appreciate any wisdom around this issue!

-Heather
 
Last edited:

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
18,150
Northern NJ

HGalindo

Member
Apr 16, 2020
11
Dallas, TX
Welcome to TFP.

Turn on Track CSI in Options in PoolMath and log your water temperature.

CSI below -0.6 can begin etching plaster with aggressive water.


Will do that, and read up on it, right now. Thanks!
 

HGalindo

Member
Apr 16, 2020
11
Dallas, TX
PoolMath says it's -.18, which is allegedly balanced. But that was a good exercise because it had my pH goal as 7.2 and that would have thrown it down to -.48, so it looks like keeping my pH where it is is my best bet. Looks like I'm also still okay as the pool heats up through the summer, as long as my other numbers stay in line. And my CYA/Chlorine balance can shift to something less wonky and it's still fine.

So, hopefully, that's enough to stem the tide. Maybe the loss we're still seeing is just residual and it will calm down over time.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
18,150
Northern NJ
Play what if with PoolMath and see the way your CSI varies as the water temperature rises.

Look at running a higher pH between 7.6-7.8, lower TA around 60-70, and CH around 350. See what that does to your CSI.
 

HGalindo

Member
Apr 16, 2020
11
Dallas, TX
Yeah, I played with temps and it stayed in "balanced" range, though closer to 0 as it warms up.

Also just messed around with the numbers you mentioned and it doesn't make a huge difference. Just 0.06 higher after shifting all those numbers. But if I do nothing else and just increase the CH by 100, CSI gets closer to 0. Though based on what I'm reading, south of 0 and above -.3 is the sweet spot. Maybe adding a little CH would make the plaster happier while staying in range? Not really sure where to continue fiddling or just leave it alone.