Understanding Chlorine burn.

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dickeystorm

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Aug 7, 2010
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Lake Jackson, TX
Hi all. Well, I just opened my pool for the season to a moderate green, :( I brought the FC up to 22 and ran the filter 24/7 and the next day it was nicely cleared. I tested at sunset and got 22 FC 1 CC and again at sunrise and got 22/.5 so I figured the shock process was complete and I could let my FC level drop to normal over the next couple of days. I forgot that my CYA was low at closing last season, and I had to add a fair amount of water over the winter. I tested tonight to see how things were doing and was surprised to see FC 2.5 CC 0. I'll run a full battery of tests tomorrow but obviously my CYA is very low.

My question is, how much chlorine will burn of by the sun with little to no CYA? Hypothetically, if my FC level was 50 could it burn off in one day of strong sun? Or is there a maximum that would burn off during the day?

On a side note my bleach supplier (walmart) has repackaged their bleach to an 8.25% concentration 121 oz bottle. The pool calculator doesn't list that size for the calculation of how much to add/what level increase you get. Is the formula available or has anyone done a conversion.

Thanks,
 
Why did you raise the FC so high if you had not tested your CYA level? That did not really follow the methods of accurate testing and dosing.

You will lose a % to the sun, at no/low CYA, that will be a very high percentage.
 
dickeystorm said:
Hi all. Well, I just opened my pool for the season to a moderate green, :( I brought the FC up to 22 and ran the filter 24/7 and the next day it was nicely cleared. I tested at sunset and got 22 FC 1 CC and again at sunrise and got 22/.5 so I figured the shock process was complete and I could let my FC level drop to normal over the next couple of days. I forgot that my CYA was low at closing last season, and I had to add a fair amount of water over the winter. I tested tonight to see how things were doing and was surprised to see FC 2.5 CC 0. I'll run a full battery of tests tomorrow but obviously my CYA is very low.

My question is, how much chlorine will burn of by the sun with little to no CYA? Hypothetically, if my FC level was 50 could it burn off in one day of strong sun? Or is there a maximum that would burn off during the day?

On a side note my bleach supplier (walmart) has repackaged their bleach to an 8.25% concentration 121 oz bottle. The pool calculator doesn't list that size for the calculation of how much to add/what level increase you get. Is the formula available or has anyone done a conversion.

Thanks,
Click to expand...
I'm not sure how fast it will burn off. I'm sure chemgeek has posted something. I do know you lose percentages, not fixed ppm, so the higher the FC, the more ppm you lose. Try the search box using terms like degradation or breakdown.

As for the new 8.25%, the only difference is that the number of jugs is wrong - it still will calculate ounces just fine if you enter the strength.

:testresults: You should always start with a full set of results! Especially when performing the shock process or asking advice about your pool chemistry. What if CYA is 150? Then your massive loss would be worrisome! If it's 10, you overdid the bleach and probably wasted a lot of it due to the aforementioned UV breakdown.
 
If there was no CYA at all, then you would lose around half of the FC per hour at peak noontime sun. Going from 22 to 2.5 would be a 50% per hour loss rate over a little more than 3 hours so it's definitely plausible (22 to 11 to 5.5 to 2.75 to 1.38, etc.). You might have a tiny amount of CYA in the water or their might not have been full sun on the pool.
 
Thanks chemgeek. I ran a full battery of tests today. There was no cya much to my surprise.
FC 7
CC .5
CH 290
TA 160
CYA appeared to be nonexistent, filled tube with no sign of cloudiness

So, I've started to add CYA. I put enough into the skimmer to get to 20 with the final goal of 40. I may go higher to combat the strong southeast TX sun. I've added a bunch of trichlor tabs in floaters for now to try and keep the FC up and to help raise the CYA.

Thanks again for the input
 
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