Calcium Drop More Than Expected

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mmcwhorter

mmcwhorter

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Jul 13, 2015
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Huntingtown, MD
Last fall when closing the pool I had a CH around 475....and this is typical as I used 73% CalHypo often (it's my preferred method for super chlorination). Before closing and after removing SWG and Robot Cleaner from the pool, I add enough Cal Hypo to get the FC up to 10-15 before the cover goes on the next day. Was surprised to open last week when the cover came off (later than normal) and see CH at 200 (tested it twice to be sure). Last fall, I drained about 8-10 inches when closing ...then added the 75% Cal Hypo and measured CH=475 when the cover went on. The water line was 6 inches below the bottom of the skimmer at that time. When I pulled the cover it was mid-skimmer level. I ran my temporary "sump" pump only 1-2 times during winter...so I don't think I removed anywhere near 50% of the water, and of course, the water removed was replaced by rain or snow. It's assumed rain/snow does not have appreciable Calcium...so I would expect Calcium to be lower, but not by one-half.

FC = 2
CH = 200
TA=80
CYA = 30
ph= 7.2 (I think I may have added a little more muriatic acid than Pool Math told me to)
Water Temp - 57F (maybe this is a clue?)

Are there any other things that would deplete CH other than draining and replacing it with low CH water? Seems a bit odd.

Don't get me wrong....I'm happy CH is not pegged....as I ALWAYS SLAM my pool with 73% Cal Hypo once I get the debris out and everything running nicely. I have learned that SLAMMING after opening virtually guarantees a trouble-free pool all season :)
 
The only scenarios that comes to mind for me is that "if" your pH was to get so high that it allowed calcium to deposit itself to the pool shell thereby no longer being in a soluble form for testing. That seems like a stretch though given the significant drop you experienced and I doubt you see that kind of scale forming. If your salt level dropped, then a leak check might be in order. If your salt didn't drop, then I would suspect it's just a testing issue. Last item to consider could be the age of your CH reagents.
 
The pH was very high when I first tested it...and I immediately added acid. With the pool open, there does not appear to be any water loss leading to a leak issue. Have not checked for scaling in the pool, given the water is still 57F today (I sure do miss Global Warming). But I'll kneel down on the coping and reach my arm down on the walls to see if I feel any. Reagents are 11 months old and stored in a cool/dry environment 24/7. I can't find my Salt Strips....my local pool store can check it, tomorrow. I need to run up there and get my yearly stash of Muriatic Acid anyway.
 
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I see Pool Math says adding 16 oz of 73-Cal-Hypo granules raises CH by 2.7 PPM for my pool (23,000 gals).
Looks like if my reading IS accurate (200 PPM), I'll need to buy some CH Raiser....I'd like to be 275-300 min.
 
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