Shock and High pH

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poolman10

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May 24, 2010
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Good morning,

Was away for a few days and returned to find a hazy green pool -- bad timing as we really need the relief during this blistering heat.

I shocked with bleach last night -- was shooting for 15.0 fc but hit 18.0 fc. The pH was a little high at 7.8, so I also added a couple of pounds of dry acid.

Checked this morning and we are at 15.0 fc, but the pH is reading 8.0+! It is a 30k gallon in-ground vinyl pool. Numbers pre-shock:

FC: 1.0
Alk: 110
pH: 7.8
CYA: 30-35

Post shock:
FC: 15.0
pH: 8.0+

Should I try to adjust the pH now, or wait until FC comes down? Also, what would be a safe FC level to allow swimming -- kids are hot and want to go swimming!!

Thanks very much for your thoughts.
 
You need to remain in the shock process until the organics in your water have been killed off. The three criteria for a completed process are passing the Overnight Chlorine Loss Test, having a CC level of .5 or less and crystal clear water. I am assuming that you have a decent test kit. According to the CYA/Chlorine Chart in Pool School the shock level for CYA 30 is 12 and for CYA 40 is 16, so you are in the ballpark there. Minimum FC to maintain after shocking would be 3 and your Target FC would be 5 (basing that on CYA 40). The general consensus around here is that you can swim up to your shock level, but not higher.
 
Thanks very much. Just checked numbers again:

FC: 14.5
CC: 0.0
Alk: 110
pH: 8

Pool is half-shaded and blue/green cloudy, and my daughter is hanging over my shoulder, saying "when?!"

So we can enter the pool with FC between 3 and 12?
 
Yes, but don't let your chlorine drop to that level until you have successfully completed the shocking process. Until your pool is clear (and you have passed the other two tests), you do not need to let your FC level drop below shock level. Make sure you have your filter running 24/7 to help clear things up.
 
Thanks Allison. Will check levels in an hour when the sun goes off the pool, add bleach if necessary, and check again in the morning to see what the overnight FC is. I can see the bottom of the deep end, but still pretty cloudy. 90+ degrees -- I want to beat this algae!
 
Will check levels in an hour when the sun goes off the pool, add bleach if necessary, and check again in the morning to see what the overnight FC is.
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That will not give you correct results. You must not add chlorine IN BETWEEN your evening test and your AM test. There is an article in Pool School that describes the OCLT.
 

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poolman10 said:
Thanks Allison. Will check levels in an hour when the sun goes off the pool, add bleach if necessary, and check again in the morning to see what the overnight FC is. I can see the bottom of the deep end, but still pretty cloudy. 90+ degrees -- I want to beat this algae!
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If your pool water is not clear, there doesn't seem to be any reason to try to perform an OCLT unless you are just curious. Instead, I would try to test the chlorine multiple times tonight (hourly if possible) and keep adding bleach to keep it at shock level.

If you are curious about the OCLT, wait about 30-45 minutes after your last chlorine addition and take a reading. Then take a reading in the morning before the sun comes up.
 
Thanks for your comments.

Dave -- I'm a knucklehead -- of course I'll can't drop bleach between readings. Thanks for reminding me.

Allison -- good point. I was at 8.5 FC after the sun went off the pool. Brushed the pool, added some bleach, and now off to pick up some more bleach at Walmart.

Thanks.
 
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