My CH level has always been in the 280-360 range. All other levels have always been stable and constant. I check weekly for TC and pH and a full TF-100 test bi-weekly. Never had a CH run up ever before. We have had lots of rain here in CA but didn't change test results before. Tested CH twice to confirm the 680ppm.
Should I just relax and keep an eye on it moving forward? Can't help but wonder why such a drastic change all of a sudden when all that has changed was a release of excessive water and my usual pH rise.

FC 6
CC 0
TC 6
pH 7.6
TA 90
CH 680
CYA 30
Temp 64
Borate 80

plaster, 17500gal, bleach

No, you should get to the bottom of it.

Welcome to the forum

680 is a little higher than you want your pool to be and a jump of 300 in just a short while doesn't happen unless you dumped about a 1/2 pickup truck load of calcium chloride in.

So, my first reaction is testing error. Were both of those conflicting tests done with the TF-100? The reported "280-360 range" makes me think that might be from a test strip.

All tests done with tf-100 kit and readings over a year have been like 280 290 310 290 260......330.
I tested twice an hour ago and just tested now the same way I always have and got a slight purple at 64 and blue at 66, drop 67 made no change from previous blue.

my tap water is CH 120 and TA 170 but autofill hasn't been an issue due to all the previous rain.

The first thing you should do is rule out testing error. Metal ions (especially copper) will interfere with the calcium test. Follow the test instructions from here or here
General Test Interferences:
Calcium Hardness Test [updated 3/10/10]



I like using 10 drops of R-0012 instead of 5, but the test should work either way.

Is there any chance that your PH was extremely low recently?

I performed the extended CH test adding the 5 drops of R-0012 to the test water before adding the R-0010 R-0011L and I get a CH 550 .

And yes, I added Muriatic acid last week with a pH 8.0 and overshot it down to 7.3 (was out and just got some from the pool store) The pH always likes to stick at 7.8 and I thought it wouldn't hurt to be on the low side since it always creeps back to 7.8 (fresh plaster in Sept. of 2010)

7.3 isn't extremely low. By extremely low, we mean somewhere in the 6.X range that would be low enough to bring calcium in the plaster into solution in dramatic fashion. 7.3 is perfectly fine and wouldn't result in the higher CH numbers that you are seeing currently.

Try the extended CH test by adding 10 drops of R-0012 first. Swirl to mix and wait 10 seconds before proceeding. Be sure to count the initial number of drops of R-0012 in the total number of drops of R-0012 needed to make the color change.

Have you been using any calcium hypochlorite?

Have you used any copper algaecide?

Have you had any calcium carbonate scaling issues? If you had scale and the scale recently dissolved, then the calcium could jump up as the scale dissolved back into the water.

The CH test in particular takes a lot of time to do properly without the speedstir. Are you taking your time, ensuring you have a lot of swirling between drops. With CH that high, I recall folks taking 5+ minutes to complete the test without a magnetic stirrer. Drop 10-15 sec swirling...Drop...10-15sec swirling....drop...

That's all I can think of in that maybe last year you took your time with completeing the test and perhaps you may be rushing to get a result...sorry if that is not the case, but really odd to see CH double without the use of calhypo

I was amazed at how much a difference using the Speedstir on the CH test made. If you don't have one you really need to swirl ~20 seconds or longer between drops to make sure you're mixing it well enough.

Just performed the extended CH test:
Fresh pool sample elbow deep,
25ml exactly in sample tube,
added 10 drops R-0012 and swirled >20 sec,
added 20 drops R-0010 and swirled the same,
added 5 R-0011L swirled,
added a drop at a time swirling over 15 sec on each drop counting the 10 drops prior and color changed from red to a faint blue at drop 58,
drop 59 produced the real blue,
drop 60 same as 59

sodium hypochlorite (Target brand 6% bleach 182oz) only chlorinator, quit using pucks back in October when my CYA reached 60 now CYA=40

never used an algicide,
Borax 20 mule team in December borates at 80 every test since using LaMotte strips,
pH level may have reached 6.8 on 3/27/11 but more between 6.8 to 7.2 when I overshot with 1 gal of 31.5% muriatic,
last test for CH was 360 on 3/20/11 before this post

Ditto. I miraculously lost CH when I started using the speedstir. Sometimes just running it another cycle without adding any more reagent will push it to the blue color. I'm just guessing, but I bet a minute of speedstir is worth three minutes of hand swirling.

divetoss,

It appears to me you are performing the test very methodically and accurately. I have absolutely no idea what the issue is. PM me your name and address...I want to send you something. (Sorry, it's not a speedstir!! )

When your pH was 8.0, your CSI would have been about +0.45, and when you lowered the pH to 6.8, the CSI would have gone to -0.55. It's possible that you had some scaling due to the high CSI and the scale dissolved when the CSI went negative.

The only other thing I can think of is possibly the drops of reagent R-0012 are inconsistent. Sometimes it helps to wipe the dropper to make sure it is clean.

Are you using the same bottle of R-0012 now as before, or are you using a new bottle?

It would only take about an 18 percent difference in drop diameter to account for the difference between 360 ppm and 590 ppm. If the original drops were 1.18 mm in diameter and the new drops were 1.00 mm in diameter, then that could account for the difference.

It is also important to hold the bottle vertically. Holding the bottle at an angle can produce inconsistent sized drops.

I have all new fresh test chemicals comming to rule out contamination and confirm results.
Will re-test when they arrive.
Thanx everyone for all the help and input!