Testing calcium hardness standard solution

bhg

Member
Nov 19, 2020
9
Austin, TX
I'm about 6 weeks in to pool ownership and TFP ways. In order to give myself some confidence in my testing I ordered the standard solution samples. pH and TA are spot on, CYA I'm reading 40 instead of 50 but found several threads on this and tips for lighting, etc. so I will try that one again.

But, the CH test is way off. I'm measuring 375 (15 drops) on the 200ppm standard solution. For my pool I read 625ppm so now don't know what to believe. I ordered the test kit back in December so nothing should be old or bad. Any ideas what could cause such a discrepancy?
 

HermanTX

Gold Supporter
May 20, 2020
1,413
Katy TX
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Chlorine
Liquid Chlorine
Great news on your testing experience. With regard to CH, are you using the 10ml sample or 25ml sample. You just say test kit in your signature so not sure which one you are using and what format you may be using. The TF-100 recommends the 10ml sample with 10 drops of R-0010 followed by 3 drops of R-0011L to turn the solution Red. Then count the R-0012 drops x 25.
Also, are you using a speed-stirrer or swirling by hand?
Just want to verify that is what we are working with.
 

bhg

Member
Nov 19, 2020
9
Austin, TX
Yes I am using the TF-100 with 10ml sample just as you described, and am using a speed-stirrer. Even tried the method of putting 5 drops of R-12 in first and the total drops were still the same.
 

HermanTX

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May 20, 2020
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Katy TX
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Apologize for getting back to you so late. It is feasible that the standard solution could be inaccurate or your reagents are bad. Your FC is under 10ppm so I do not think that is an issue. Not sure if you have a water softener but if you do, test your tap water (in the house) to see if you have CH. It should be zero thus the solution will go straight to blue. If you do not have a water softener, still test your tap water to see what that reading is. I am not sure what Austin water is supposed to be in CH but maybe you can look at a test report the city may send out quarterly. Tap water in Katy (west of Houston) is in the 100-150ppm CH range.

I am asking Marty @mknauss to review your post to offer any suggestions on your CH test regarding the standard solution vs. pool sample.
 

mknauss

Mod Squad
TFP Expert
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May 3, 2014
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Laughlin, NV
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Testing at 375 versus a standard solution of 200 is a large discrepancy. Do take your time adding the R0012 drops. The color change can be slow to form. I typically start and stop the Stir device between drops as I approach what I expect will be end point. It seems that action pushes the color change. Also be sure your reagent bottle is vertical, and you are not squeezing it. Let the drops form and fall off the bottle tip.
 

bhg

Member
Nov 19, 2020
9
Austin, TX
Thanks, guys, for the replies. So I took the tip off of the R12 and rinsed it with tap water. I could tell the drops were bigger today than the other day when I did the test, and I took it extra slow to make sure they fell off by themselves. Today I got 10 drops or 250ppm so feeling better. I guess it does prove some benefit of the standard solutions to test my testing technique. The pool tested to 400ppm now.

And I did take Herman's advice as well. I do not have a water softener. City of Austin report shows 13ppm for "Calcium" and 90ppm for "Total Hardness (as CaCO3)". Not sure which of those translate to our test but I tested CH to be 75ppm on my fill water. Is that low enough to keep me in a reasonable range throughout the season without drifting up?

I need to bump CYA up a tad but I'm getting close to getting everything in TFP "ideal range" before my first season gets going.
 
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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
36,390
Laughlin, NV
Pool Size
6000
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Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Use rain as often as possible to refill the pool due to evaporation. Monitor CH monthly. Good job!
 
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