Calcium hardness keeps dropping

mdames

Active member
Apr 7, 2017
29
Northridge, CA
I have a 17,000 gallon plaster pool. The Chlorine level is 3.0 (I use trichlor pucks), PH is 7.6, TA is 65, CYA is 45. My problem is I can't keep my calcium level above 200. I keep adding calcium chloride to the pool. It raises the calcium level to about 205. Within 2 days I'm at 190, and it keeps falling from there. This has been going on for about 2 months now. There is no discernible leak. My pool is not used at all. Any ideas about why the calcium level keeps falling? I live in a Southern California valley. Summer temps are in the mid to high 90's. Any help is appreciated. Thanks

Mike
 

thetekgeek

Bronze Supporter
Jun 8, 2018
164
Nebraska
I haven't come across an issue like this before. Typically, CH builds up in a pool rather than disappears from the pool. I see that your fill water is 40 CH in your signature, do you have an autofill? If so, it is possible that you are either losing a fair amount of water to evaporation or a leak and it is being replaced by much lower CH water.

What are the rest of your levels? Can you post a full set of results? I have a vinyl pool so I don't worry about CH much. Plug your full test results into PoolMath and see what the calculated CSI is, if it is within recommended range for a plaster pool it might not be something you have to chase too much.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,396
Laughlin, NV
The only way to reduce the CH level in pool water is to physically take some water out and replace it with water having a lower CH.

Evaporation does not remove calcium.
 

mdames

Active member
Apr 7, 2017
29
Northridge, CA
I do not have an autofill. It seems to me that I am losing a normal amount of water through evaporation. I typically add water to the pool about every 5 days or so in these very hot and dry summer months. I add about 1.5 inches each time. This is what it has typically been for the past two years. So it doesn't appear to be leaking. I should mention that I had the pool re-plastered a little less than two years ago. My other pool stats are already in the body of my first post.
 

setsailsoon

LifeTime Supporter
TFP Guide
Oct 25, 2015
1,461
Stuart/FL
M,
That's baffling. I agree with Marty's comments. Almost seems like test results are in question. How are you maintaining CYA level? Typically treating with pucks causes CYA to climb. Are you seeing this and removing water to control CYA? I've used Lamotte lab reagents in my previous life and found them to be reliable but I've never used the system you have. Let me see if an expert on everything related to weird chemistry can offer anything @JoyfulNoise can help. Matt, what say you?

Chris
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,798
Tucson, AZ
I don’t trust ColorQ’s when it comes to CH. There have been far too many posts over the years of pool owners swearing their CH is all over the place and the minute they ditch the ColorQ and use titratable reagents, bang!, suddenly the levels are correct. It’s too easy to mess up a light absorption measurement either with bad reagents, old cuvettes and/or aging/flaky light sources/detectors.

Post Taylor test kit results and then we can discuss the issue.
 
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duraleigh

Admin
Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
32,734
Sebring, Florida
JoyfulNoise is absolutely on target. The years of reports on this forum have demonstrated the colorQ to not be as accurate as TFP likes.....especially on CH.
 
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RMcGirr83

Gold Supporter
Nov 19, 2018
398
Tuscola, TX
My Color Q is pretty consistent with CH tests, albeit low compared to titrating with the Taylor kit. I use the Color Q for chlorine, pH Alky and CYA. Taylor for CH. While the Color Q will never match the results from the Taylor (one is more precise than the other). Using both and comparing, they're pretty much in line with each other which is good enough for me. This isn't fine furniture :)
 

AUSpool

Bronze Supporter
LifeTime Supporter
TFP Guide
Sep 23, 2015
654
Brisbane, Australia.
Interesting, you would think then that the readings from the ColorQ would be higher than titrating, no? It's the exact opposite.
Very true, it should read higher if there is magnesium ions present. In natural fresh waterways Mg is normally around 20-35% of the total hardness. But pools are not natural.

The colourQ has no pre treatment step for magnesium and therefore actually reads total hardness. I asked LaMotte directly and they confirmed the same. It shouldn’t read less, the fact that it does (spin thingy included) is a good reason why we’re a pit sceptical of the results.

We/I should go back to Mike and ask if he’s seeing any abnormal drops in any other parameters?
 

mdames

Active member
Apr 7, 2017
29
Northridge, CA
Thanks everyone. Well..... I purchased a Taylor complete kit for testing my pool. I have just taken the measurements using the Taylor kit and the LaMotte. The Chlorine, CYA, and TA are quite close to being the same. However, the PH and Calcium Hardness and WORLD'S APART! LaMotte shows 7.6 PH. Taylor says it's 8.5. LaMotte is 198 for CH, and the Taylor unit is 570. Which one do I believe? My CSI using the Taylor kit is 1.04! My CSI using the LaMotte is -.23. If Taylor is correct, I need to get my PH down quickly. Also, if my CH is 570, I have a question. Is that high level OK as long as my CSI is in the acceptable range? By the way, my pool is clear. My other measurements: CL - 3.5, TA - 70, CYA - 52. It looks very good. Thanks
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,798
Tucson, AZ
My guess is the light source or the photodetector in the Lamotte unit has gone out of calibration or has become defective. Your ColorQ is showing both a low signal as well as drift over successive measurements. You can call LaMotte up and see if they will service the unit. If the cuvette has been used a lot, it may be dirty or defective. Check the expiration on the reagents as well.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
9,718
Northern NJ
I'm estimating it is 8.5. It showed it was a little more than 8. Should I trust the Taylor result for PH more than the LaMotte?
When pH tests over 8 on the Taylor we don’t estimate. We put 8 in PoolMath with a target of 7.6 and add that much MA. Wait 30 minutes and test again. If pH still over 8 repeat until pH is in the 7s.

What is your FC? Is it less than 10 according to the FAS/DPD test?