Calcium Hardness Test - Issue with New/Old Chemicals

shanebo

Well-known member
May 25, 2017
118
Southern NJ
Need advice on some recent weirdness with my CH test. I've been using the TF-100 for the past three years. First kit was purchased in Spring 2017, refill purchased in Spring 2018. I did not buy a new kit last year because I had plenty and the reagents last two years. Bought a new kit this year (full kit).

Over the past 3 years, my CH has consistently tested between 250 and 350 each week. From splashing, backwashing, winterizing, etc., it might drop to 275, and I'd add some calcium chloride to get it up to 325-ish. I haven't added that much -- maybe 8 lbs or so per year over the past three years (4 in the spring, 4 in mid-summer). Last test with the old reagent showed a CH of 300, which is about where I like to be.

I got my new TF-100 test kit in the mail last week. First test with the new reagents showed CH of 650! Thinking I had screwed something up, I did another test and got 600. Worse, my TA was showing 120 (PH and TA always run high in my pool from waterfall, fountain, waterslide, and kids -- I typically add 1 gal of acid per week during the summer). It started raining so I gave up. Yesterday, I ran the tests again, slowly and methodically, side by side with the old reagents. Test with the old reagent showed CH of 300. Test with new reagent showed CH of 525. Notably, the change from red to blue with the new reagent was not instantaneous, as it was with the old -- I would drip, swirl, and then the solution would change color 10-15 seconds later. I ran both tests again, this time swirling then waiting 10-15 seconds before the next drop. Got 300 again with the old reagents (instant change), 525 with the new (~15 seconds after 21st drip and swirl).

Anyone have an idea what's going on, and what my real CH levels are? My first thought was that the ~2 yr old reagents had gone bad, and that the new reagents are giving me the accurate results. But the delay in the color change combined with the more consistent results from my old reagents have me second guessing myself. No new visible scaling and my CSI is currently OK, but I have been adding acid more frequently to keep the PH down and the CSI within recommended range. Appreciate your thoughts.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
It's possible that your old reagent simply isn't giving your the accuracy you need. I would also say that there is no need to wait so long between each drop. A drop about every second or so is fine. To rule out potential metal ion interference, you could try the modified CH test as follows:
The sample may turn purple during the test, or go to blue for a moment and then turn back to red/pink. This is called a “fading endpoint” and is caused by interference from metal ions. If this happens, do the test again, but this time add five drops of R-0012 before adding any R-0010 or R-0011L. Remember to count the initial five drops in the total.
In extreme cases, a fading endpoint may occur even when adding five drops of R-0012 at the start. If that happens, mix pool water with an equal quantity of distilled water, test that, and then multiply the result by two.
As always, make sure you get past all the colors: red/pink > purple > then all the way to baby blue.

 

grottoguy

LifeTime Supporter
Aug 24, 2014
458
NJ
Need advice on some recent weirdness with my CH test. I've been using the TF-100 for the past three years. First kit was purchased in Spring 2017, refill purchased in Spring 2018. I did not buy a new kit last year because I had plenty and the reagents last two years. Bought a new kit this year (full kit).

Over the past 3 years, my CH has consistently tested between 250 and 350 each week. From splashing, backwashing, winterizing, etc., it might drop to 275, and I'd add some calcium chloride to get it up to 325-ish. I haven't added that much -- maybe 8 lbs or so per year over the past three years (4 in the spring, 4 in mid-summer). Last test with the old reagent showed a CH of 300, which is about where I like to be.

I got my new TF-100 test kit in the mail last week. First test with the new reagents showed CH of 650! Thinking I had screwed something up, I did another test and got 600. Worse, my TA was showing 120 (PH and TA always run high in my pool from waterfall, fountain, waterslide, and kids -- I typically add 1 gal of acid per week during the summer). It started raining so I gave up. Yesterday, I ran the tests again, slowly and methodically, side by side with the old reagents. Test with the old reagent showed CH of 300. Test with new reagent showed CH of 525. Notably, the change from red to blue with the new reagent was not instantaneous, as it was with the old -- I would drip, swirl, and then the solution would change color 10-15 seconds later. I ran both tests again, this time swirling then waiting 10-15 seconds before the next drop. Got 300 again with the old reagents (instant change), 525 with the new (~15 seconds after 21st drip and swirl).

Anyone have an idea what's going on, and what my real CH levels are? My first thought was that the ~2 yr old reagents had gone bad, and that the new reagents are giving me the accurate results. But the delay in the color change combined with the more consistent results from my old reagents have me second guessing myself. No new visible scaling and my CSI is currently OK, but I have been adding acid more frequently to keep the PH down and the CSI within recommended range. Appreciate your thoughts.
I always compare my results with the new chemicals each year to the results with the old ones. This year I noticed that my calcium hardness test with the new chemicals was 275 and the CH with the old chemicals was 200-225. I repeated the test by using some of the old chemicals and some of the new chemicals until I was able to isolate the problem. My new R012 was the chemical causing the disparity. If I used the new chemicals but substituted the old R012 I got the same result as if I used all the old chemicals. It took me several tests to Identify the culprit. I suspect the new R012 is the problem and I have been meaning to order a new one. It is also possible that the tip of the new R012 is permitting smaller drops than should be the case but I haven’t examined that yet.
 

shanebo

Well-known member
May 25, 2017
118
Southern NJ
It's possible that your old reagent simply isn't giving your the accuracy you need. I would also say that there is no need to wait so long between each drop. A drop about every second or so is fine. To rule out potential metal ion interference, you could try the modified CH test as follows:


As always, make sure you get past all the colors: red/pink > purple > then all the way to baby blue.

I agree with everything you said, and I've never waited so long between drops on this or any other test. But it doesn't explain why the color of the solution changes about 15 seconds after I've added the 21st drop ...

Thanks for pointing out the fading endpoint issue. I read about it this morning on the forum, and I'll re-test using that process to see if it changes anything. I've seen that happen before (temporary "cloud" changing from red to blue/purple and back), but this is a slightly different issue, in that the solution stays red for several seconds after the drop, then turns to blue. Very curious.
 

shanebo

Well-known member
May 25, 2017
118
Southern NJ
I always compare my results with the new chemicals each year to the results with the old ones. This year I noticed that my calcium hardness test with the new chemicals was 275 and the CH with the old chemicals was 200-225. I repeated the test by using some of the old chemicals and some of the new chemicals until I was able to isolate the problem. My new R012 was the chemical causing the disparity. If I used the new chemicals but substituted the old R012 I got the same result as if I used all the old chemicals. It took me several tests to Identify the culprit. I suspect the new R012 is the problem and I have been meaning to order a new one. It is also possible that the tip of the new R012 is permitting smaller drops than should be the case but I haven’t examined that yet.
Good to know. I had assumed that it was the 11L (the thick, dark fluid) since that's the one that usually gives me problems. But now that you mention it, one of my new reagents shot out a thin "stream" rather than a drip when I first tried to use it -- I replaced and tightened the cap and restarted the test and everything looked fine -- it very well could have been the 12 giving me smaller drops. I'll have to check that out. Spending $5 on a new reagent would be great news, far better than draining and refilling the pool in the middle of summer, lol!
 

OTPirate

Admin
In The Industry
Oct 2, 2013
1,569
Creedmoor, NC
Make sure not to squeeze the bottle, hold it perfectly vertical and let the drop form on its own. Also, you can switch it out with another tip (rinse with water in between) to see if there is any difference. They are designed to snap on and off easily.