Total Alk and Calcium Hardness questions.

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mlawrence17

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Aug 3, 2010
81
Charleston, South Carolina
This is my first pool and the plaster was finished about 4 weeks ago. I've maintained the levels without any problem with the help of this forum, but now I'm turning on the SWG and noticed that the recommended levels for TA are a little lower for SWG systems than for bleach. (SWG = 60 - 80) (Bleach = 70-90+). I'm at 100 which was a tiny bit high with bleach, but seems much more out of wack with salt. So I was thinking of lowering it, and went back to pool school where I read this:

"There are two reasons to lower your total alkalinity (TA) right away, because you want to slow down the rate that the PH rises, or if high TA is contributing to a high calcium saturation index (CSI) which puts you at risk of calcium scaling. You shouldn't lower TA just to reach a target number. Make sure you actually have one of the above issues before lowering your TA. "

So....am I supposed to lower it...or not?
Also, since this is my first pool, I've got to ask one stupid question. I've noticed that my CH level is constantly going down. Is it possible to make it more stable or is that just what happens with a plaster pool?
 
Something's going on in your pool - CH never goes down by itself.

It is either coming out of solution and forming scale on the walls or the water is being diluted. Dilution can be a huge amount of splashout, a lot of backwashing, or a leak. You need to figure this out. Do you have an auto-fill? Do you manually have to add a lot of water? Has CYA also been going down?

Test results would be helpful here - particularly pH. High pH can cause scaling.

Back to the TA question: a SWG will tend to drive pH up, so you are probably (or should be) adding acid fairly often. If you consistently keep pH in range, TA will go down, ever so slowly. Unless you keep adding higher TA fill water, which brings us back to the question of a possible leak.
 
I haven't added any water, in fact I've drained about 9" off over the past week or two, because we've been getting so much rain. My CYA level dropped from 52 to 40.
It's not like its dropping from 300 to 50 or anything. I had it at 254 about two weeks ago and last night when I checked it...it was 190. My PH was 7.9 last night, so I added a little acid. Maybe I'm over reacting and it just seems like it's dropping a lot since raising it requires so much calcium chloride.
 
mlawrence17 said:
I haven't added any water, in fact I've drained about 9" off over the past week or two, because we've been getting so much rain. My CYA level dropped from 52 to 40.
It's not like its dropping from 300 to 50 or anything. I had it at 254 about two weeks ago and last night when I checked it...it was 190. My PH was 7.9 last night, so I added a little acid. Maybe I'm over reacting and it just seems like it's dropping a lot since raising it requires so much calcium chloride.
Click to expand...
Well that explains the missing CH.

40/52 on the CYA = 77%
190/254 on the CH = 75%

Well within normal test variations. Curious how you got 254 on the CH test, though. Typically it's by 10s or 25s. CYA is usually a guesstimate between the 10 ppm graduations. You're not relying on pool store testing, are you??? Hmmmmm?
 
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