Chlorine Lock

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fort384

Active member
Apr 27, 2019
36
Illinois
Hi there,

I have been fighting chlorine lock since opening this spring. I thought I had it under control, but this week it has reared its ugly head again...

It started off shortly after opening... I could get total chlorine reading off the scale, but free chlorine was reading 1-2 ppm max. I tested cyanic acid both with a strip as well as titration, and both tests read 0 somehow (even though last year my pool remained balanced with little intervention - and my pool was pretty much full upon opening after all the snow melt). IT was drained down to below the skimmers before closing, so the fill up was due to snow melt.

I got some stabilizer to remedy my 0 reading on cyanic acid, and added 8 lbs to my 25,000 gal system. The following week, free chlorine and total chlorine were roughly equal, at around 3. Cyanic acid was reading around 40-50 with titration, still 0 with the strips.

Two weeks later, my cyanic acid tests at around 80-90 ppm (with no additional stabilizer added), still says "0" on the dip strip - thinking the strips are just totally inaccurate.

It seems like my cyanic acid reading should not have increased that much with 8 lbs of stabilizer added. And now I am back to chlorine lock - shocked the pool yesterday, total chlorine is reading 10 ppm or so this evening after an intense day of sun, free chlorine is reading near, if not, 0.

Total Alkalinity is testing within normal range, as is total hardness. pH is a little low, I need to get some pH up this week, it is reading 7.0. Two weeks ago it was 7.6 and I added a pint or two of acid to bring it down - I am not sure if the acid dropped it to a low reading or if something else is going on there.

Any ideas what I should do next here? This is only my second year with a pool... last year it was so easy, pH was perfect all year, and free chlorine was easy to keep at 1-3ppm with a shock every other week or so (and inline chlorinator to maintain in between). Speaking of the inline chlorinator, last year I kept the dial at around "3" to keep free chlorine/total chlorine in desired range. This year, I have it set at 6-8 and still low or no free chlorine almost all the time.

Pool is basically spotless - I have a robot that runs through the week most days. A little bit of tree junk here in the spring, but the skimmers get emptied every day, and I have a VS pump that runs 20 hours a day. Water looks extremely clear, no signs of algae or anything. I even changed the cartridge filters last week just in case it was because of filters collecting organic material during the spring start up. Swim load is pretty low - it doesn't get used much during the week, and gets a few hours with a few swimmers on the weekend. It just doesn't seem like I should be seeing this much chlorine demand and it points to a chemistry issue instead. I test the water several times a week, do maintenance nearly every if not every day. So it certainly isn't from neglect :).

Open to any suggestions or requests for additional info.
 
No such thing as Chlorine Lock, its just a pool$tore tactic to get money out of you pocket. Please read up on ABCs of Pool Water Chemistry and order a Test Kits Compared so you can get accurate and reliable results. Guesstrips just dont work. If you had high CC and 0 Cya you could have developed ammonia during the winter. For now just add 5 ppm of liquid chlorine per day until your kit arrives. Download the PoolMath app so you can track your numbers.
 
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I have a Taylor test kit. I also have the strips just for testing just the hot tub over the winter. I am fairly confident in the titration test results I detailed. I even replaced the test solution for my CYA test just to be certain. I have tested it multiple times. It consistently reads 80 or so the last several days. The weird thing is the original test results showing 0, and then over a 2 week period jumping to 80 ppm with only the addition of 8lbs of CYA. I really don't intend to switch to liquid chlorine - I prefer using tabs in a chlorinator that require a lot less intervention... plus I am not gonna start lugging jugs of chlorine around. I mentioned this is only my second year with this pool, but I grew up with a pool as well and for 10+ years used tabs and inline chlorinator with little to no problem. I have never been to a pool store... So I am not sure how a pool store is scamming me to get money out of my pocket. Chlorine lock seems to simply mean that FC is reading low while TC is high or normal. If you'd like me to call it something other than chlorine lock, that is fine. Let's just say I have high TC and low FC, and a weird CYA reading that doesn't seem to match actions (though as I said I am pretty confident in the results as they have been repeated multiple times during all stages of this issue over the last month and a half or so.

I did use the poolMath app last year but have found it isn't really necessary to log all of it. I test my pool religiously and am fairly aware of the levels with some confidence as a result. What I am not confident in is what could cause the type of swing I have seen this season, and the best course of action to alleviate the imbalance. If I need to start replacing some of the water, that is fine... I am on a pretty deep well, and the water table is high. It just doesn't seem like 80ppm CYA should be enough to cause this much of an imbalance without something else going on.
 
That means you have
FC 1
CC 9
Please update your signature with your test kit so we dont have to guess. So it seams you been around a while and know TFP methods. This should be easy for you, just follow Poolschool database.
 
So, something is off. The volume of your pool, the initial CYA reading wasn’t actually zero... something.

Everything is clean? Ladders, light niches, etc.?

Can you post a picture of your pool?

The other thing is this - you stated that you aren’t interested in any method besides the pucks. The next thing i would advise you to do is follow SLAM and use Pool Math to guide you in the right amount of chlorine to use for your CYA while you are SLAMming. But if you don’t want to follow the advice of this site, I’m not sure how else we can help.
 
Your CCs are high, FC is low, and CYA is now reading 80. I can't explain why you had a 0 reading before and now have 80, but likely it was an issue with the initial test (you said titration for CYA in your first post in addition to the strips? There isn't a titration test for CYA that I'm aware of, just the refraction test with the black dot).

Our solution for this is going to be to follow the SLAM Process, but as you said you aren't willing to use liquid chlorine, we really can't assist. Your tabs are going to keep driving your CYA up, and you'll eventually get an algae bloom as your FC isn't able to get anywhere near high enough to work with the higher CYA. The "pros" who follow the pool store methods (whether or not you go to one) will tell you you have chlorine lock / high TDS / old water / whatever they want to call it and that you have to drain and refill - which will bring your CYA down, and the tabs will start to work again as your FC/CYA ratio gets more in line. But keep using tabs, and you'll head right back to high CYA levels and another drain.

So - your call. If you don't want to use liquid chlorine, then a SWG is the way to chlorinate that doesn't add CYA (or CH) to your pool. But even then, you occasionally need to add some liquid chlorine as the SWG is for maintenance doses, not for clearing up any issues...unless you test the water carefully and often to be sure the FC is always in line. But if tabs is all you're willing to use, then you aren't going to get advice here that will really be of any use to you.

Good luck!
 
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Fort,

TFP methods use liquid chlorine to avoid the build up of CYA. So long as you understand the CYA/FC relationship and maintain appropriate TC level this can work. We have a few members that for one reason or another do not want to use liquid chlorine. My brother's not a member but he does this because he's go a very large pool and can't use liquid chlorine dosing system. He watches CYA level closely and drains regularly to make sure he stays inside the TFP ranges. Tablets also allow him to maintain pH with almost no MA addition. He's been doing this successfully for years after he learned the hard way to watch his CYA level. Before he learned about this he'd go through multiple nasty, expensive and time-consuming algae blooms several times per year. Since he learned about FC/CYA he hasn't had any issues at all. Just a big water bill. As your CYA creeps up you'll find you use a LOT of tablets to maintain target but this can work. Just optimize partial draining frequency with tablet consumption and watch it closely. If you do this you'll be fine. If it was my pool I'd switch to SWG but you should do what you're happy with.

Good luck and let us know if there's any way we can assist.

Chris
 
Thanks for all the replies - so given my CYA is already high, I pretty much have no choice but to drain some of the water to lower it right? Even if I switched to liquid chlorine, before it will be effective I need to lower CYA?

I am on a well so I am willing to drain water every now and then - of course even with a filter on the hose I am sure that will introduce potential other issues like metals?

Also you are right - I called it titration but it’s actually the black dot refraction test.

is there any kind of automatic dosing for liquid chlorine? Cost doesn’t concern me as much as some convenience. perhaps a hybrid solution utilizing my inline chlorinator for low level maintenance, supplemented with liquid a few times a week?
 

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Automatic dosers for liquid chlorine are called stenner pumps. A few folks on here have them, and I think in general are happy with them. But a TON of people use saltwater generators (SWGs) for automatic chlorination. I just installed one myself about a month ago, and wish I had done so years ago.
 
I saw someone asked for a photo. Here is what it looks like. I am in process of replacing about 10% of the water. Not enough I’m sure but I figure I can do 10% a couple times a week for the next few weeks and should eventually get CYA down to 30-40. Unless there is a better way. I figure this can keep the pool clear and usable at least since I am not having other issues at present.
Is Walmart the best place to by liquid?
D0302B9D-FC5E-488E-AC62-51D03035EE46.jpeg
 
You are in Illinois, so the best place to buy liquid chlorine is Menards. A gallon of 12.5% is currently $3.55 after their "11% off everything" rebate. There MAY be a BOGO sale starting on July 4th. There traditionally is, but they didn't have their typical last-week-of-April BOGO this year, so the July sale may not happen either.

 
fort384 said:
Any reason to avoid this? https://www.farmandfleet.com/produc...I59SwibX86QIVC2yGCh2aKQOUEAQYASABEgLIPfD_BwE#

Looks like a good price and close by.
Click to expand...


Just make sure you buy whole cases still in the cardboard boxes. Those places tend to open the cases and sit the jugs out in the sun,

While I have discovered that dosing daily with liquid and manually testing and controlling my chem levels results in truly a "trouble free pool," it is a bit of a PITB to do it everyday and the options for being away for a few days are limited to asking the sweet lady across the street to dose for me (which she always has) or using a floater.

With that in mind, I am in the process of installing a Stenner pump for my pool. I chose the Econ T model with a timer. I purchased an Ammo box for a pump housing and bought a 12-gallon barrel off of FB Marketplace for $10. All in I have about $325 in the set up. As soon as can get to the store and assemble the rest of the plumbing parts I need, I am going to install it. I will post a thread of the process.
 
Ok, thanks. I will pick some up today. Based on the math, it looks to be actually pretty economical, once I can actually get my CYA in line. Given that I am not having any algae trouble at present and water is relatively clear, should I dose up the water to high levels a la SLAM, or just try to maintain while continuing to do some drain and fills over the coming weeks to reduce CYA?
 
fort384 said:
Ok, thanks. I will pick some up today. Based on the math, it looks to be actually pretty economical, once I can actually get my CYA in line. Given that I am not having any algae trouble at present and water is relatively clear, should I dose up the water to high levels a la SLAM, or just try to maintain while continuing to do some drain and fills over the coming weeks to reduce CYA?
Click to expand...


If you are confident that your combined chlorine is that high, I would definitely SLAM the pool. There something in there consuming it.
 
Some people manage their CYA at a high level, like 80 or so, but it takes a lot of FC. See the FC/CYA Levels. If you ever have to SLAM it would be a LOT of chlorine to maintain at that high level. Day-to-day, you'd have to make sure it never falls below minimum, but would have to get close to test the pH because the pH test is invalid over 10ppm of FC.

What is your current FC / CC / CYA with the Taylor kit?
 

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