CH is the worst test....

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voidpointer

voidpointer

Gold Supporter
Oct 8, 2020
543
Prosper, TX
Pool Size
19440
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
I know I've posted about this before. I got some really great advice, in particular the notes section from this page:
www.troublefreepool.com

Calcium Hardness

A drop-based test that measures the hardness in your water. Once measured, it is used … Read more…
www.troublefreepool.com www.troublefreepool.com

I put 5 drops R12 before the test and I don't really feel like that's helping anymore. It's getting difficult to know when to stop putting drops in, because the solution takes sooo long to change to blue. If I stop the drops for a few seconds, I can see the color slowly changing to blue as it is being stirred (I'm using the magnetic stirrer). There's another point in the notes about adding in distilled water. Do I need to consider doing this? CH is already such a pain in the rear...

The past two months I've gotten a CH reading of about 600. I don't feel confident that is accurate due to my uncertainty on when to stop putting R12 in. I usually go very slowly and wait for it to fade to blue, but the color changes are so subtle it's difficult to tell. This test feels more subjective than CYA at this point!

Assuming my CH of 600 is accurate, I'm getting nervous about it getting to high. I guess I'm just not getting enough rain. I haven't done a drain of my pool yet, nor do I know the procedure to do that, nor do I know when I should consider doing it (like, how far out of the recommended range should I let CH go).

What can I do to make CH testing more accurate, and is it more difficult to test as the CH gets higher? I don't remember it being this hard to test when it was a few hundred less...

And when do I need to worry about my CH levels? I know I'm not quite at the recommended max yet but i'm seeing a steady increase...
 
Cut your pool water sample 1:1 with distilled water. Must be distilled water. Then do the test and double the results.

Once you get into high CH levels, it is difficult to see the endpoint. Especially with any metals in the water.

Harvest as much rain water as you can. Once your CH rises above 600 ppm, it begins to be more of an issue to keep a slightly negative CSI.
 
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You and I have the same fill water, so would be hard to imagine your CH is 600 unless you have been using Cal-hypo or adding CH. Have you done either?

Depending on where you are in Prosper, I don't mind a quick in person test / comparison against my TFPro. (I'm East side).
 
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JJ_Tex said:
You and I have the same fill water, so would be hard to imagine your CH is 600 unless you have been using Cal-hypo or adding CH. Have you done either?

Depending on where you are in Prosper, I don't mind a quick in person test / comparison against my TFPro. (I'm East side).
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I don't use cal hypo or add CH. Is it possible it came from my plaster? I may have been using too much acid for several months. I was adding about 32oz every 2 days to keep up with the demand. There's marks on my plaster where I pour acid into the pool. I'm not sure if that's from me or the plaster job. Maybe I'm paranoid. I can't think of any other reason.

I'll try diluting with distilled water and if I still get confusing results, I'll take you up on your offer. I'm even happy to bring a sample to you to save you the trouble. Thanks for helping!

I'm hoping the CH goes down over time on it's own as I get spillover from the rain. I only add 12oz acid every 2-6 days now. Acid demand seems to be much lower in the winter. I also make sure to brush longer after pouring it in. I haven't seen CH increase since then, at least.
 
It certainly could have come from your plaster, especially with newer plaster. 2 things jumped out from your post:

1. Why are you having to add acid so often? pH will certainly rise on its own, but will increase with agitation of the water. Do you have water features, spillovers, or anything else that runs a lot that is raising your pH?

2. If you are seeing marks on your plaster from adding acid, that can be problematic as it is dissolving layers of plaster and will shorten the life of your plaster/pebble. When adding MA, it should be done in front of a return in a deep part of your pool, poured slowly, and poured with your pump running.
 
JJ_Tex said:
It certainly could have come from your plaster, especially with newer plaster. 2 things jumped out from your post:

1. Why are you having to add acid so often? pH will certainly rise on its own, but will increase with agitation of the water. Do you have water features, spillovers, or anything else that runs a lot that is raising your pH?

2. If you are seeing marks on your plaster from adding acid, that can be problematic as it is dissolving layers of plaster and will shorten the life of your plaster/pebble. When adding MA, it should be done in front of a return in a deep part of your pool, poured slowly, and poured with your pump running.
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I asked about #1 early on. My pool finished construction and opened in March 2023. Since then, I was aiming for about 7.5 pH. In about 2 days, it would go back up to 8.2. I do not run water features unless people are in the pool. Spillovers, bubblers, sheers -- they're all off. My understanding is that this is just "hungry plaster" due to the new construction. And that in about a year or so, it would fully "cure" and not demand so much acid.

Regarding #2, I'll admit I got impatient pouring so slowly. One thread I saw on the forum gave me an idea. Just pour the acid in quickly and brush after to spread it around. That's what I've been doing every time I add. I do pour in front of a return and on the deep end.

Again I'm not sure if the discoloration is from the acid I'm adding or not. The plaster had a bunch of marks on it after first application; it's hard to tell if marks came from poor construction or something I did. The marks run toward the drains at the center bottom of the pool so I assume that water just ran down the plaster after they applied it.
 
mknauss said:
Cut your pool water sample 1:1 with distilled water. Must be distilled water. Then do the test and double the results.

Once you get into high CH levels, it is difficult to see the endpoint. Especially with any metals in the water.

Harvest as much rain water as you can. Once your CH rises above 600 ppm, it begins to be more of an issue to keep a slightly negative CSI.
Click to expand...
I added 10ml of distilled water.
Then I added 10ml of pool water up to the 20ml mark.
I added 10 drops of R-10
Then 3 drops of R-11L
Then I got up to 19 drops of R-12. I do feel the shift to blue was quicker this time.

If I am doing the math right... 19 drops times 25 time 2 is 950ppm of CH??

I'm not sure if that's right.
 

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When you used double the sample size (20ml), you cut the drop strength in half to negate the 50/50 sample dilution. So your 19 drops were 25 each for 475. That's within the 1 drop variance and with 2 consecutive tests agreeing, I'm sold its correct (450 to 475).
 
Thank you for confirming that. Makes me feel much better about this test now. I also want to try the 5 drops of R12 at the start with the diluted 10ml to see if that makes the endpoint even easier.
 
voidpointer said:
Ah, I see. So do the 20ml sample and pour 10ml of it for the test. Could I do 5ml each instead?
Click to expand...

No, that wouldn't be the same. The idea of the dilution is to reduce the concentration of substances that can interfere with the test. The price you pay is a less sensitive test (50ppm per drop instead of 25ppm per drop).

If you just test with a 5ml sample without dilution, you're just paying the price of getting a less sensitive test without getting the benefit of reducing test interferences.
 
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