Trouble with free chlorine loss

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S

shackwrrr

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May 26, 2015
27
piedmont,oh
Recently converted from baquacil and had passed all tests to finish conversion. Replaced sand and added CYA. Over the next week the pool began using chlorine extremely excessively. Went from 1/2 gallon a day to now about 2-3 gallons a day.

Ph 7.2
Cya 40
alk 140
calcium 160

For the last week I have been bringing pool to a slam FC of 16 morning and night. In the morning I usually have 5-7 ppm of FC from the night before and in the evening it's usually at 0. So its using about 10 FC overnight and 16 through the sunny day. I have brushed and swept to no avail and the pool water has stayed crystal clear the whole time. There has been a little bit of "dirt" on the bottom that dissapates as soon as I brush it, I sweep it and it still comes back. It showed up after covering the pool with a tarp that had sand on it so I assume it is just silt. I am trying to get this pool balanced enough to install the SWG that I got. There have been periodic swimmers like one person every 3 days and I got in to brush the walls at one point.

Also what has been weird is that CC has remained 0 or .5 the entire time, I would figure with that much chlorine loss that some more CC would show up.

Any help is appreciated.
 
Your fairly large and rapid loss with a clear pool sounds like something chemical, not algae. I suspect some source of remaining Baquacil is now reacting with the chlorine, but I don't know where it's coming from. There's not much you can do except maintain the SLAM until you oxidize through whatever it is -- at least unless you identify where it's coming from to remove it some other way.

CC only shows up if the intermediate CC chemical is more rapidly produced from chlorine than it gets oxidized from chlorine. There are quite a few chemicals that get oxidized by chlorine such that their slow step forms CC while their fast step breaks it down so you won't see any significant CC in that case.
 
Mmmm. That is strange to be so delayed. Aquafinesse shouldn't interfere -- those are just surfactants and they don't react with chlorine -- certainly not as much as you are seeing. Very weird. You replaced the sand so it shouldn't be the filter.

Was a light removed from a light niche or a ladder removed or any other equipment where there might have been a volume of water that wasn't seen before?

If the loss were just during the day then that can be from no or too little CYA (but you have 40 ppm) or from bromide in the pool so really a bromine pool, but you are seeing significant loss overnight so that isn't it.

Did the problem start after putting anything into or onto the water, such as the tarp you mentioned? Are you still using a tarp or a cover on the pool? If so, I'd remove it and see if the chlorine demand drops.

If you used a metal sequestrant with EDTA then that would increase chlorine demand. If you used an algaecide that used ammonia or an ammonium compound, then that would increase chlorine demand. If you used a linear quat algaeicde, then that would increase chlorine demand (Polyquat does as well, but not that much). If you had an overly powerful ozonator, then that could lower chlorine but would have to be pretty darn big. If you had a massive UV system that could lower chlorine but again it'd have to be pretty darn big.

A bunch of urinating kids could increase chlorine demand but in your 10,000 gallon pool it would take extraordinary amounts for what you are seeing so I don't think that's it either.
 
No lights, the only 2 things in pool are the ladder which was in the pool when I passed the oclt during baquacil conversion and a cover which is a unrecognized blue bubble cover. I don't see any obvious signs of the cover degrading.

6/16 I tested FC at 13ppm around 10:30 pm.

6/17 at 6:15 am it was 6ppm -added 1 gallon 10% to bring it to 16ppm

6/17 8:30 pm 0ppm added 1.5 gallons 10% and brushed pool will test at 10 pm to set up for oclt.
 
Well I'm at a loss. If it was just during the day then I'd suspect the CYA reading was wrong and really closer to zero, but with the large nighttime loss something is clearly consuming a LOT of chlorine. I don't believe we've ever seen this before, certainly not from a Baquacil conversion. The loss rate is similar to when there's been a bacterial conversion of CYA to ammonia after the ammonia part has been removed but you haven't had any significant CC and you haven't had any mysterious CYA drop so I don't think that's it.

Has any other water chemistry parameter been changing? You mentioned soda ash and baking soda, but those were just added after the Baquacil conversion to get the pH and TA in range, correct? You haven't seen anything other than FC changing a lot, have you? pH, TA, CYA, CH (unlikely)?

Check your skimmer, your pump basket, and maybe even your filter just to see if there's anything in them, though I can't imaging what would cause the amount of chlorine demand you are seeing. Even dead animals don't create this kind of demand.

You know, there were a very few number of reports over the years of people adding CYA to the water and had a huge chlorine demand though not instantaneous (very similar to what you are seeing and what happens in the later stages of a bacterial conversion of CYA where there is partially degraded CYA). We determined that it was a "bad" brand of CYA so wasn't really CYA (a lot of CYA is imported from China and once in a while a manufacturer tries to get away with something or doesn't have good quality control). I wonder if that's what happened here since it seemed to start up after the Baquacil conversion and after you added the CYA to the water. Do you recall what brand you used? Try testing CYA again and see if you get the same number you got before. If it's dropped, then perhaps the CYA degraded and chlorine has been oxidizing it. That's not good and for 48 ppm CYA that was added it would take around 120 ppm FC to get rid of (if none was pure CYA and all were something else like biuret, allophanate, or urea).

By the way, 4 pounds of soda ash and 4 pounds of baking soda in 10,000 gallons would together raise the TA by 74 ppm. That sounds like a lot since you probably started out with some TA to begin with. That's probably how you got to 140 ppm -- you could have stayed at 70-80 ppm. As for 4 pounds of CYA, that should add 48 ppm CYA to 10,000 gallons so that seems consistent.
 
Last year when I converted from Baquacil I had a similar experience.

The water was clear but the pool was consuming a very large amount of chlorine. I was also trying to kill some odd white "bio mass" type of "white water mold" for lack of a better name.

I kept after it and finally like someone with a bad fever it finally broke. After that and since the pool has been great and it has held FC and has acted just like one(s) from this site would expect.


What I wish I would have done
1. Was check for ammonia with a inexpensive test kit (like for aquariums Walmart etc). (If I could only go back in time, It would be nice to have ruled that out.)
2. Been more diligent about frequency of checking slam level. (check more often)
3. In hindsight - drained the pool and started with fresh. (however I would not have seen how well the TFP method works and has educated me on pool maintenance. I am a true believer)

Hang in there. You may feel like you are going crazy but once you get past the mass consumption of Chlorine your pool water will act correctly and you will be pleased.
 
I have been on vacation for a week but while I was gone I had my mom test and add chlorine once a day. She was adding 2 gallons every night to bring FC up to 20ppm and it is still dropping a lot overnight. From 8pm last night till 10:30 today (very overcast and rainy) it lost 14 pom.
 
I picked up an ammonia test and it tested zero so that's not the problem.

Chem geek, is there any materials like plastics or rubbers that could eat up chlorine? I haven't had a chance to try it without the cover on it but I wonder if that could cause issues.

The other thought is that during the conversion from baq, we diverted water from a nearby roof into the pool, not sure what's up there that would Leach chemicals.
 

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Yes, chlorine will oxidize pool covers, but usually the rate is slower than the loss rate you see. For my automatic pool cover it's probably around 0.5 ppm FC per day at the most. I suspect that for typical bubble-type covers it's something similar. It may be that you have a strange cover that chlorine reacts with more. You can certainly remove the cover, especially during an OCLT, to see if that may be the cause.

As for the roof, it's possible it had something that got into the water you used, but if that's the case it's taking quite a while for chlorine to oxidize it.
 
The ladder has an open backside. We used it for a week last year before pulling it out. It sat in the rain/snow/sun all winter just hanging over the edge of the deck. I sprayed the dirt off of it before I put it in this year. I've been super busy, I want to pull the ladder and cover the do an oclt to see what it does.

Sent from my SM-G900V using Tapatalk
 
Haven't posted in a while but I seem to have it beat. Put 2 gallons in Thursday morning brought it up to 20ppm, tested again Friday night and it was around 12ppm Tested Sunday morning it was at 5 and tested this morning it was at 3ppm. Tonight I'm doing official oclt and then adding salt for chlorine generator
 
Not sure if it helped or hurt but about the time I got the pool to behave I had ignored the pool for about a week, Ph climbed to about 8.4 (probably over that from rain aeration) and FC dropped to nothing for about 6 days. I then dumped in 2 gallons to bring it up to 20ppm and thats when it stuck and started working ok. Never were any cc's.
 
Either whatever was causing the excess demand went away (seems unlikely though) or you coincidentally got rid of it around the time you ignored the pool for a week. I don't know of anything where ignoring a problem had it go away, but who knows. The good news is that your pool is behaving well again.

You are just lucky that bacteria didn't grow and convert your CYA to ammonia. That can happen if you let a pool go for too long and that would create a HUGE chlorine demand. I speak from personal experience about that in It Can Happen to Anyone - Zero Chlorine, CYA-->Ammonia.
 
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