Shock again?

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S

smuggs

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LifeTime Supporter
Sep 10, 2007
141
Gloucester County, NJ
I shocked on Sunday night with 6.75 gallons of 6% bleach which should have brought my FC to about 16. My numbers before shocking were:

FC 0
TC 0
pH 7.4
Alk 100
CH 250
CYA 45-50

I puposely brought the Cl levels down to do an acid treatment on a suspected stain. I did the treatment on Thursday morning. On Saturday evening, I added 1.5 gal of 6% bleach and had .5 FC and 1.5 TC, so I suspected there was something besides the sun eating my FC and decided to shock on Sunday night. After coming home from work on Monday evening (I didn't have Columbus Day off like my kids and the Gov't), I tested the water and got these results:

FC 1
TC 4
pH 7.5
Alk 100
CH 250
CYA 45-50

It was very hot yesterday, so I expected some burn off. Unfortunately, I couldn't do anything during the day to try to keep the levels up as I was at work and my wife is 38 weeks pregnant. I plan to test again tonight, but it seems that I need to shock again as I plan to keep the pool open just a few more weeks to be able to do some laps at night and use the spa....hopefully my wife will be able to use the spa a few weeks after giving birth before we close up for the winter. Thoughts?

P.S. - I found some really cheap 6% bleach at Aldi ($0.99 for 92oz)
 
Yes, you should shock the pool. In addition to the unusual chlorine consumption you appear to have a CC level of 3, which needs to come down. Shocking means adding chlorine to your shock target level (which depends on your CYA level, 15 or 16 in your case), and holding that level by retesting and adding more chlorine to maintain the level until the FC level holds overnight by it's self and CC goes to zero. If the water is clear this will usually go very quickly.

If you just did an ascorbic acid treatment, the ascorbic acid will consume a bunch of chlorine at first. If you did an ascorbic acid treatment to remove metal stains you should be careful about bringing the chlorine level up too quickly.
 
Your chlorine is getting eaten up by the ascorbic acid treatment. I would not birng the levels up to shock, unless you think you may have algae- bringing the chlorine to shock may bring the stain back :shock: What you have to do after the ascorbic acid treatment is to keep the level of chlorine at the high end of your cya very consistantly, which for you would be 6 to 8ppms. You should also bring your ph down to 7.2 - it will help make the chlorine more powerful, and will lessen the chance of the stain coming back. If you have a sand filter or DE filter, you can keep a chlorine puck in the skimmer basket - DO NOT do this if you have a cartridge filter. Make sure you keep your filter runing 24/7 until the chlorine holds overnight. Your chlorine will not hold until all of the ascorbic acid it used up by the chlorine. The trick s to be very consistant with keeping your levels up without having to shock. You should not shock for at least a week after an ascorbic acid treatment and two weeks is better :) Let me know if you have any other questiions
 
Mbar - to clarify, should I be concerned with getting total chlorine to 6-8ppm or free chlorine to that level?

As for algae, I don't think I have a problem...water is clear, but did notice a couple dark marks on the deep end wall this morning that I don't recall seeing before.
 
The Mermaid Queen is right :) we usually mean free chlorine, however, with just doing the ascorbic acid treatment you can be getting a cc from the acid breaking down. If your water is clear, I would keep the chlorine level at 8 for now - check the black spots you are seeing - if it is an organic stain, it shoud clear up if you rub a trichor puck on it - or put some powdered chorine in a sock and rub on the stain. If it lightens or clears, then you will have to shock. If you have to shock, then take the ph down to 7 and shock, keeping the filter running 24/7. If it doesn't clear with the chlorine you can put some ascorbic acid in a sock (or crushed vitamin c tablets), or some ph down in a sock and rub on the stain. It will lift if it is a mineral stain. If it is mineral, then take the ph back down to 7 and add some sequestering agent, keeping the filter running 24/7. So check the stain, and let me know what you find out, and I can help you through it :)
 
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