CH test reads 0?

[waterbear]

Yes, and it does not work. Like I said before I was playing around with it and found that it worked with about 8-10 drops of the indicator and I cross checked the results with the Taylor kit I have a few times and it is pretty close that way.

[Tootie]

I' am very puzzled,when I did the test a few day's ago,it did just what it supposed too.After reading the post again this morning I did another test,and wouldn't you know, it never turned violet?????
We had a pretty good temperature drop and my water is only in the 40's,compare to the other day when it was in the 70's...
Could that be a problem with it???I' am no Expert,and really have a hard enough Time to understand all the other stuff going on in the pool...But now I' am very confuzzeld...

Ok,I had to check again before I post,and no it did not work,just like Waterbear said it took me 9 drops,and then it turned in more like a black grayish color????



@Sisie5,I have the Instructions.....

I will try to scan and post them




Margit

[cygnusecks]

Well I'm also quite confused. I just re-did the test, and it only took 2 drops to turn the violet color. And then it too 10 drops to make it blue, which means my CH is 500ppm. Hmmm.. The only difference is that the pump hasn't kicked on today, so the water has sat motionless in the pool for about 13 hours. Could that alter the tests in any way?

Is 500ppm a bad thing? My TA is 60.

[prh129]

I don't have my kit with me so I can't post a photo, but the one I got at Walmart was an HTH (5-way I believe) test kit, not the Aqua Chem shown above. I'm also pretty sure I had to add 5 drops of the blue reagent for hardness. My pool sample did not turn blue but rather a yellow color and after a lot of drops of the second reagent it slowly turned green then sort-of blue. I re-tested on my tap water (which was not used to fill the pool) and it turned blue right away. I received the PS234 kit and that hardness test started with a third reagent - with the PS234 the hardness test worked on the pool water as expected and the hardness was pretty low. It looks like in my case there was something in the water that caused a problem with the 2-reagent test but not with the 3-reagent test (that's probably why the third reagent was added)

The Cl/pH tester in the HTH kit looks the same as the one in the PS234 kit.

Peter

[PoolDoc]

. . . but the one I got at Walmart was an HTH (5-way I believe) test kit, not the Aqua Chem shown above. I'm also pretty sure I had to add 5 drops of the blue reagent for hardness. My pool sample did not turn blue but rather a yellow color and after a lot of drops of the second reagent it slowly turned green then sort-of blue.

That's the kit made by Taylor. The testblock in the OTO version *IS* the same as the one in the PS234, and the calcium reagents are the same, as well. 5 drops is the normal quantity of indicator dye for the calcium test.

But, there are (or should be) THREE reagents in that test:

1. a buffer, used first
2. an indicator dye, used second
3. the test reagent, used third. These are the drops that need to be counted carefully.

If you tried to do the test, using the dye first, and the test reagent second, you would get wierd results. But, that said, I've never heard of a yellow to blue transition on the calcium test. That transition DOES occur, on the alkalinity test, with VERY high levels of chlorine, or on PHMB pool with high levels of peroxide.

Ben
"PoolDoc"

[waterbear]

Hmmm.....just repeated the test myself and then checked it against my Taylor kit and a test strip. Here is how it went:
Aquachem kit
added 2 drops and water turned yellow( as it has in the past with 2 drops). Continued adding drops until it turned violet red...took 14 drops.
titrated and got 350 ppm (7th drop turned blue, 8th drop no change).
repeated test with 20 drops of indicator and got between 300-350 ppm (6 drops changed to blue but 7th drop made it a bit deeper, 8th drop no change)

Taylor kit...got 200 ppm which is what I believe it should be based on what it was last test and the amount of calcium chloride I just added to the pool recently. (Yes, I know you don't need calcium in a fiberglass pool but my fill water has 0 ppm calcium hardness and I have a heater)

tested with a strip which tests for TOTAL hardness (calcium and magnesium hardness) and got a bit higher than 250 pppm total hardness (strip color chart goes from 250 ppm to 1000 ppm...not much accuracy here)

Now I wonder if the Aquachem kit might be testing for total hardness and not calcium hardness. The Taylor test for total hardness is a 2 reagent test. (indicator and titrant)

Also, the last time I tried this (my CH level was at 140 with the Taylor) it only took 8-10 drops of the indicator to get a violet red color and the results were much closer to the Taylor test...I assumed it was the difference in accuracy of 10 ppm for the Taylor and 50 ppn for the Aquachem.

Anyone have any thoughts on this?

[PoolDoc]

It looks like in my case there was something in the water that caused a problem with the 2-reagent test but not with the 3-reagent test (that's probably why the third reagent was added)

You win the prize!

I was careless, and didn't notice on my quick read through earlier. The '2-reagent' system combines the buffer and the indicator. But, on pools with lower pH, and relatively high alkalinity, there's not enough buffer in the indicator. That's why extra drops of indicator -- which add extra drops of buffer -- works, when the 'normal' number of drops don't.

(The pH of the sample has to be pretty high, for the indicator to work, and the 'buffer' tries to move the pH up high enough to work. But, pools with high alkalinity are resistant to pH change, thus the problem.)

Ben

[waterbear]

You win the prize!

I was careless, and didn't notice on my quick read through earlier. The '2-reagent' system combines the buffer and the indicator. But, on pools with lower pH, and relatively high alkalinity, there's not enough buffer in the indicator. That's why extra drops of indicator -- which add extra drops of buffer -- works, when the 'normal' number of drops don't.

(The pH of the sample has to be pretty high, for the indicator to work, and the 'buffer' tries to move the pH up high enough to work. But, pools with high alkalinity are resistant to pH change, thus the problem.)

Ben

So this could also explain my last test results. If the pH is not brough up high enough then the interfering magnesium would NOT precipitate out (or not completely) and the titration would show more of a total hardness reading instead of a true calcium hardness reading! (Current ALK at 110 ppm and pH at 7.4) When I did the experiements previously my pH was at 7.8-7.9, ALK 110. My ALK never seems to change much unless I really lower the pH and airate.

Bottom line, IMHO, is that the test in the Aquachem kit is not reliable for CH!

[prh129]

At the time I did the HTH hardness test with the weird results (yellow solution to faint green), my pH was low and so was my alkalinity. (I did the test twice with the same result both times - as I swirled the blue reagent the wisps turned red before disappearing.) The numbers at the time were:
pH - 7.0
TCL - 2.5
ALK - 30 ppm

I have since brought the pH up (7.3) and the alkalinity up (90) also. I will repeat the HTH test tonight and see if it still acts weird.

Peter

[prh129]

I re-tested with the HTH kit and got the same weird result - the sample had a faint yellow tint after the 5 drops of hardness indicator (which is listed as 23% isopropanol and 77% Triethanolamine).

I tested with the PS234 and after 20 drops of cal 1 and 5 drops of cal 2, the sample was pink. After two drops of cal 3 the sample turned blue. This makes sense and is about what I would expect.

I then started over with 20 drops of cal 1, then 5 drops of the HTH indicator and the sample turned pink although deeper than with cal 2. I then tried the HTH titrant and after 10 drops it was more of a greyish color but nowhere near the blue from the last test. I repeated this test using cal 3 as the titrant this time and got the same grey result so it is clearly the HTH hardness indicator that is not working with my water for some reason.

I also tested pH (7.3) and alkality (90) on the sample.