CH rising?

[DONNIE]

Ok. Ok. Took extra care to fill my test bottle to exactly 25ml. Let stand (capped) for 1 hour to get to room temp. Added 2 drops of titrant before test. Added the 5 drops of blue which took about 30 seconds to totally mix. Started adding my drops very carefully to be exact. At drop 41 (counting the first 2) it turned slightly purple. drop 42 turned a distinctive blue. Drop 43 & 44 produced no change. So voila...CH=420ish. I guess the 41 degree water made the difference. Or maybe it was the wine! Lesson learned. DONT TEST 41 DEGREE WATER! Thanks Richard. Thanks Carl. I appreciate the concern and especially the guidance.

Donnie

[waterbear]

I've said it before and I will say it again, water temp makes a difference. If you compare test results done of 75 deg water and 45 deg water you will be comparing apples to oranges! Taylor doesn't really specify a temp at which the tests should be done (to the best of my knowledge) but LaMotte does state that their reagents are formulated to produce accurate results between 70 and 80 degrees.

[DONNIE]

Just for kicks I tested Ph, FC & CC last night both at 41 degrees and a couple of hours later (from a sealled container) at room temperature, aprox 72 degrees. All tests came out exactly the same. I know now not to test CH and TA unless they are at room temp as the results come out completley different that at 41 degrees. I havent tried salt at the two different temps but my test at 41 degrees and my SWG are the same. In the future I will always test at room temperature to get consistent results. Thanks Guys.

Donnie

[waste]

Donnie, you're doing a great job with your new pool and thanks for the input!

[chem geek]

Donnie,

Great minds think alike. I did exactly the same thing after you posted your CH results. Like you, I found that chlorine tests did not appear to be temperature dependent. In fact, the chlorine test seems to be TIME dependent where waiting too long to do the test has the chlorine level drop so it's more important to do the test quickly than to have it be at room temperature.

I did not get the same results as you did with the pH test. I found the pH to drop as the water warmed up and that is actually what I expected since there are technical reasons that should be the case. It doesn't drop that much, however, since it theoretically is only around 0.1 unit from 50 to 70, but from 45-50 to 85 it should be around 0.2 units which is much more noticeable. I heated the sample in my hand to simulate "heated" pool water and got the pH to drop more noticeably (I also kept the container covered during the test to prevent "natural" pH rise from outgassing).

I also didn't find as much variation as you did with the CH test. I did find a small variation, but only a couple of drops difference (i.e. 20 ppm) which isn't much.

I am somewhat conflicted regarding recommending that ALL tests be done at room temperature. I think the pH test is best done at actual temperatures since pH is supposed to vary with temperature and the chlorine test loses accuracy if you wait too long. So perhaps, all tests but pH and chlorine should be done at room (or "warm" water, if in the summer) temperature or if you let water warm up for the chlorine test -- cover the container while waiting.

Richard

[DONNIE]

Richard, Do you use the standard Taylor Ph color test or do you use something more elaborate? I may have had a small difference but not a noticable one. What do you anticipate the salt test results will be a cold vs warm temps will be?

Donnie

[chem geek]

Richard, Do you use the standard Taylor Ph color test or do you use something more elaborate? I may have had a small difference but not a noticable one. What do you anticipate the salt test results will be a cold vs warm temps will be?

Donnie

I just use the standard Taylor pH colorimetric (i.e. "match the color") test. I did a salt (chloride) test on my pool, but only did it at one temperature. I was surprised to find that I had between 800 and 1000 ppm salt in my pool since I effectively diluted by 50% twice two winters in a row, though not last winter nor this winter, and I've only used chlorinating liquid -- only about 0.5 ppm per day in the summer and hardly any demand at all in the winter. So I expected around 500 ppm or less. I must have had a MUCH higher TDS than I thought in the past. Either that or the salt test is temperature dependent. My guess is that it isn't. The silver nitrate is a pretty strong one-way reaction so I wouldn't expect the indicator change to be very temperature dependent. Of all the tests, it's the CYA test that is probably the MOST temperature dependent (due to the partial solubility of melamine cyanurate, though see this post for more info about that).

Richard

[DONNIE]

Thanks Waste. I'm really having fun now that I am understanding whats going on with my pool. It's really a fairly basic science that everybody (including myself) finds overwhelming at first. The more I learn, The easier it becomes.

Donnie