Why is the Plaster Discoloring?

[tmarcoux]

My pool has always struggled with high pH. It seems I could add acid to it every day, but every other day at a minimum. Of course, when I traveled, it could go unattended for a 3-4 days and over time, scale formed on the waterline tile and the gray plaster began to turn blotchy white. So this winter, I drained the pool and had an acid wash to clear up the scale, and a contractor to blast off the waterline scale. It looked MUCH better.

When I started it up, I decided to not run the SWG and use BBB using bleach, including borates. Everything appeared normal, and I added my salt and began running on my SWG. Over the past month or two, I have monitored the pool daily. However, I have slowly seen the blotching coming back and now I am seeing spots the size of quarters that are very white. When I scratch at them, there isn't anything apparent on the surface. In addition, I am seeing small mineral deposits forming in the shallow end and spa. They are similar to small drops, which I can scrape off. They are definitely a mineral.

Here are my questions:
1. Why am I battling pH again? I added 30 oz acid yesterday to get me from 7.8 to 7.5, and today it's back at/over 7.8? I will easily hit 8.2 tomorrow. This is with the spa overflow off to minimize aeration.
2. Why is this color leaching out of the plaster? It's especially bad in the shallow end.
3. Why can't I stop this mineral deposit from forming?

Here are my readings from today:
TC/FC = 4
CC = 0
pH=7.8
TA=70
CH=275
Borates=40
Salt=2900
CYA=50 (I plan to increase to 70, but I'd like to figure this out first)

I had hoped adding borates would help with the pH drift - it hasn't but it has increased the amount of acid needed to balance the pH and consequently the co$t of chemicals.

 

[Casey]

The SWG is contributing to your high pH. If you don't keep the pH down, it will cause the calcium scale you are seeing.

 

[tmarcoux]

What would you recommend for the low and high range. When the pH hits 7.8-8.0 I bring it down to 7.5. But again, I could almost do that daily. Should I be driving it down more? If so, will I be driving TA down as well?

Using the SWG I am adding acid at half the amount of bleach I was adding (maybe a bit less). But the cost difference is high. Is this normal?

 

[karmabiker]

Assuming a tempo of 88 ( that's what mine is in houston) it puts your CSI at -0.13 which should NOT be problematic. There are a couple of things that could be going on ... but I suspect a bum plaster job. Check out this post by OnBalance:

http://www.troublefreepool.com/threads/41414-Ten-Guidelines-for-Quality-Pool-Plaster

If you don't have any recourse with the plaster co I would start targeting a lower pH to keep your CSI down in the -.4 to -.6 range. "Safe" (we are talking about a normal pool surface here) is -.6 to +.6 for the CSI. To find your current CSI plug all of your numbers into pool math (IGNORE the recommended CSI level - that is the "what it will be if you adjust all of the other level to their recommended range - not a recommendation for a particular CSI level).

The 4 biggest players in CSI are CH, pH, TA and temperature. Personally I would play with the pH first- start targeting the 7.3-7.4 level and see if the problem persists.

How new is the plaster?