UV light rapid free chlorine level dropping

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Chem geek,
Uv was unplugged 3 days ago. I believe this is why I have been able to keep FC levels. My CYA before this was 45 so even if +/- factor of 10, the FC target level has been excessed for 2 days. Are you say I may need to raise this target higher than CYA/FC chart. Then how do I determine the correct target? What level should I raise the Fc to? There has been no bather load for 2 weeks. water temp 82, that leaves Sun UV & organics. so if we can't measure or rely on the incomplete oxidation as CC due to the addition of more Chlorine releasing any that maybe bound then are there any or factor to look for? I have tested for ammonia----none. My CYA is constant. what am I missing. The backyard smell of a chlorine factory & my family is calling me the chlorine man….water is crystal clear.. but I can not now just maintain the <1ppm overnight loss to complete SLAM. Does the high Nitrate level interfere with chlorine? Thanks
 
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I might be getting slightly confused...let me see if I can sort this out...

1. You aren't testing why? Gotta test to be "maintaining" the slam - aka the shock level...that is a necessary part of making...

2. Slamming is not over unless you have LESS than 1 ppm overnight chlorine loss...while keeping at FC 4-6 and .5 cc is normal, losing more than 1 ppm FC overnight is not and requires slamming

3. If there's any chance you have that bacteria that converts cya to ammonia, see those threads chemgeek linked to get a better sense of what kind of chlorine useage they were talking about to knock it out.
 
Thats my point. no CYA loss or ammonia present. I stop testing because loss was constant in the 3 hour window so just added 1 gal every 3 hours to maintain > FC target & continue SLAM process. just tested FC:22 CC:0 so without CYA loss or ammonia present would you increase Fc level 8x the CYA/FC chart level from 20 x 8 160ppm…..
 
I'm totally confused at this point as well. You were reporting many ppm FC losses per hour before, so are you saying that now you don't see that since you turned off the UV system? What exactly is your FC loss rate overnight now You say you still have > 1 ppm FC loss overnight at SLAM levels of chlorine (or regular levels -- that wasn't clear), correct? So is your CYA level 45 ppm and you are trying to maintain a SLAM level of 18 ppm or so?

You aren't understanding the CYA loss -- we were talking about BEFORE you opened your pool, not now. The CYA loss before, which was substantial, could have been at least in part bacteria converting it to ammonia. If you looked at the link I gave earlier then you would have seen my post where it took me 56 ppm FC cumulatively added before the pool would hold chlorine at normal loss rates and yet the maximum CC I saw was 1.6 ppm. I only measured ammonia initially, but not later on. An ammonia test would only be valid if NO FC was holding at all. Once FC still measures at all even for an hour (i.e. it can drop, but doesn't go to almost zero), then the ammonia test is not useful. So forget about ammonia and your low to zero CC at this point. Focus on FC loss which can still occur from oxidizing the remnants of the degraded CYA from bacteria (if that's the cause).
 
yes chem my CYA is 45, my FC target is 20. Last night at 10:30pm FC:21 at 6:30am FC:14 so the loss was 7ppm overnight. the last 2 day I have tested every hour to maintain that >20ppm level. I am now able to maintain that level for 3 hours instead of only 1 hour. FC levels, except overnight has not gone below 20ppm. I raised the FC level to 34ppm to see if that would extent holding time. I have added 56gal of chlorine over 3 days…every hour first two days(except o/n) then every 3 hours today. so how do I find a level above the recommended FC level(>20) to target with a CYA of 45? I am only focused on a FC shock level to maintain, only testing FC at this point. If 20ppm is not the level what is the correct process to determine that level? just keep adding every, what interval? until FC level does not go down or as you say "before the pool would hold chlorine at normal loss rates". Thanks for the help.
 
The level you are at is fine and is working to get rid of whatever is left to get oxidized. I suspect it may only be a few more days or perhaps a week before it gets to a point of being tolerable at normal chlorine levels. You might still have higher than normal loss, but hopefully not that high and eventually it should get to a more typical 2-3 ppm FC per 24 hours loss.
 
Wow. Well, if you have losses that high the you aren't as close as I thought. You reported that last year your CYA was 90-100 to 135 and now it is 45 so at a minimum there was a loss of 45 ppm CYA. If all of that was broken down by bacteria to partially degraded CYA (some may have been ammonia, but you are long past that), then that would take at least 110 ppm FC cumulatively added to get rid of and if your CYA were actually 135 and now 45 then the 90 ppm CYA loss could require 220 ppm FC cumulatively added. Do you have any idea of how much FC you have cumulatively added so far? This is one of those situations where water replacement would have been better (at least to significantly dilute if not replace) unless water is more precious than the large amounts of chlorine we are talking about.
 
last Aug 2013 the pool store measured CYA 137!! I had some water displacement over the winter and had to add 5,000 gal of water. First test 2014 CYA:35… I have added 95gal at 5ppm each thats 475ppm chlorine…. But 34gal or 175ppm were with UV light on…. which greatly accelerated the chlorine degradation. Once the UV light was D/C the chlorine loss slowed & I was able to hit & hold FC targets, but still have the 7ppm losses overnight. I will continue until the 16 remaining gal are used,unless the math says i"ll never get there... what is the calculation for CYA loss & the required amount of chlorine ppm?
 
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For bacterial conversion of CYA into ammonia, every 10 ppm CYA becomes 3.26 ppm ammonia and that takes roughly 26 to 33 ppm FC to oxidize. So figure that every 1 ppm CYA takes roughly 3 ppm FC to get rid of.

I'm concerned with how much chlorine you've added, even accounting for the UV which I also find hard to believe that it consumed THAT much. So did you figure out if you lower chlorine overnight if the pump is off? If you don't have a large chlorine drop unless the circulation is on, then the problem is in the circulation system -- likely the filter but could be in the pipes. Did you ever look at your filter to make sure there weren't biofilms in it or otherwise cleaned them?
 

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I have not left the system off overnight, will try tonight. I have cleaned the filters as per the site instructions of wash off soak in TSP wash, then acid soak wash> i did notice after the acid wash an opaque to greenish cast floating in the acid solution. The filters look ok. will remove today…What bacteria is capable or usually found or responsible for this??
 
OK then, the problem is in the bulk pool water itself, unfortunately. You might consider doing some water change over time (partial drain/refill) if you don't see any more progress in having the chlorine loss diminish. I would think that if this were just from CYA degradation that the chlorine demand would be declining, but though it did earlier it doesn't seem to that much right now. Up to you what to do -- a pretty rare situation. We've seen high demand before, but usually it tapers off substantially in a week or two. On the other hand, there was another thread recently where there was chlorine demand for a month and then it seemingly disappeared without much explanation.
 
I too am mystified. In your shoes I might look up mustard shock level and try that for a day BUT IN A BUCKET beside the pool to see if the dose made a difference in breaking down whatever the heck you're fighting before you send the chlorine company's kids through college ;)

With the UV off and a "normal" non-shock level of chlorine, I'd be interested in seeing what your percentage of loss is daily. Your 3-hr average seems to be about 30%.

I wish we knew how to help you, but a bucket test to minimize cost and experimentation/extrapolation is all I've got ;)
 
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