Chlorine lock or bad Chlorine tabs?

dearliza98

Member
Oct 10, 2019
7
Nashville, TN
Hey all. I’m both new here and a new pool owner. We put in an in-ground pool this summer and it’s been great. My water was perfectly balanced until recently. This may not be great but I had been using Clorox brand 3” stabilized tablets with no apparent issues. I recently switched to In The Swim tablets and my chlorine levels dropped immediately. I literally have 0 readings in both free and available chlorine despite more than enough tablets in the floater. I used several brands of test strips and also a water testing kit to verify this. My other chemical levels are within range and look correct.

The pool shop says I have chlorine lock so I drained part of the pool, refilled and tried again. Still no chlorine readings. In The Swim says its not defective tablets. So I used a non-chlorine shock to oxidize the water. No clue if that worked because I still have no chlorine readings.

I shocked with chlorine shock and I do now have chlorine levels showing which makes me suspicious that I don’t have chlorine lock and that my In the Swim tablets are defective.

Does anyone have any advice? Should I buy another brand of tablets to see if I can maintain chlorine levels?
 

Bama Rambler

Mod Squad
TFP Expert
Bronze Supporter
LifeTime Supporter
Jun 22, 2009
23,627
SouthWest Alabama
First, you do not have chlorine lock! Simply because there's no such thing. Spend a little time in Pool School and you'll learn a great deal.
Second, You should quit using tablets period and get a good test kit so you'll know exactly what the problem is. (Hint: It isn't chlorine lock) :)
Third, I know; everybody says get a good test kit, It really is important. So, get a good test kit. The TF-100 is the best.
Fourth, Don't get defensive about what I've said above. We all started not knowing and we all have been pool stored. Stick around here and learn all you can and then decide how you want to maintain your pool. We'll only judge you a little if you decide to stick with tablets :) , but at least learn what you're dealing with. And you'll see that there's a better way.
 

wireform

Silver Supporter
In The Industry
Aug 15, 2017
482
Spring Valley, NY
You have an algae problem consuming your chlorine. You need to read pool school to see why you shouldn't use tablets. Start using liquid chlorine and get yourself the tf-100 test kit.
 

dearliza98

Member
Oct 10, 2019
7
Nashville, TN
@Bama Rambler @wireform Thank you both for the info. I am by no means married to the tablets... that's just what the pool company told me to use.

After doing some homework, I realized that I've just been dumping stabilizer in there with every tablet and probably created this issue. However, I do have a liquid testing kit (not the TF-100) and my CYA levels appear normal.

Anyway, I see liquid chlorine is recommended and I browsed Pool School and learned that common household bleach is acceptable to use. I'm interested in trying this and figuring out how much I'll actually need to use to maintain 3-4ppm. I'm told my pool is 20,000 gallons but my calculations online seem closer to 24,000 gallons with the 8' deep end.

I hear you loud and clear that I need the TF-100 testing kit and I'll be purchasing that. Wouldn't mind some more advice on whether you think I should partially drain/fill to somewhat reset with fresh water or if I may be able to use what I have.
 

JJ_Tex

Bronze Supporter
Jul 17, 2019
398
Prosper, TX (DFW)
Usually you only need to drain if you have high CYA or something else in the water you want to get rid of.

You said your CYA was normal, but didnt say what that was. Once you get a CYA reading, round up to the nearest 10 (ie a reading of 45 is 50), then use the CYA chart to determine your correct chlorine level for every day and also SLAM if you need that for algae.

 

Demegrad9

Well-known member
May 27, 2017
359
Coventry, CT
The pool shop says I have chlorine lock so I drained part of the pool, refilled and tried again. Still no chlorine readings. In The Swim says its not defective tablets. So I used a non-chlorine shock to oxidize the water. No clue if that worked because I still have no chlorine readings.
The myth of 'Chorine Lock' (and yes it's definitely a myth) is not that no matter how much chlorine you dump in you still test 0 chlorine. The myth is that you have and test high chlorine levels but you are still getting algae or cloudiness or whatever. The typical case is that a pool owner tests their water and/or takes it to their pool shop and the water test shows that all the chemicals are perfect but they still have problems getting or keeping their pool clear. So since the professional at the pool store doesn't have a good answer they substitute a bad one, "Chlorine Lock"!!!

This pool shop is impressive bad, even worse then your typical shop. They don't even know how to apply their own bad advise.
 
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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
10,550
Northern NJ
Anyway, I see liquid chlorine is recommended and I browsed Pool School and learned that common household bleach is acceptable to use.
Make sure the bleach you use is plain, unscented, not splashless, no additives, and not Clorox with Cloromax Technology.

I'm interested in trying this and figuring out how much I'll actually need to use to maintain 3-4ppm.
We use PoolMath to calculate doses and effect of adding chemicals.

It will take 150oz of 6% bleach to add 3ppm to 24,000 gallons of water.

I'm told my pool is 20,000 gallons but my calculations online seem closer to 24,000 gallons with the 8' deep end.
With a good test kit and PoolMath you will see if adding chem has the expected effect and dial in the gallons.
 

dearliza98

Member
Oct 10, 2019
7
Nashville, TN
@ajw22 Thank you for the liquid bleach and pool math details. I had no idea how hard it is to find just regular bleach. Everything I'm seeing online (Walmart, Lowes) is either splashless or has the coloromax technology... Do you have any secrets where to find the regular stuff? I'm going to switch to this as soon as I find a source for it!
 

undrwater

Active member
Do you have any secrets where to find the regular stuff?
Your pool supply store may have liquid chlorine. Just go in and ask for it and don't walk out with anything else (unless it's a brush or something). Walmart in my area has 12% pool chlorine as does Home Depot and Lowe's. There's a thread somewhere on this site titled "where to buy chlorine" that has some location specific details that might be useful.
 

JJ_Tex

Bronze Supporter
Jul 17, 2019
398
Prosper, TX (DFW)
Our walmart has the 10% liquid chlorine, but I've heard people have had good luck with the Great Value brand bleach. Around here you can get liquid chlorine at Lowes, Home Deopt, and even Kroger plus you can always get it at a pool store.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
10,550
Northern NJ
@ajw22 Thank you for the liquid bleach and pool math details. I had no idea how hard it is to find just regular bleach. Everything I'm seeing online (Walmart, Lowes) is either splashless or has the coloromax technology... Do you have any secrets where to find the regular stuff? I'm going to switch to this as soon as I find a source for it!


This time of year the chlorine stock gets thin. I use the stores websites to see what stores around me have it in stock and then reserve it with an internet order to pickup in store.
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
11,536
Evans, Georgia
With a pool as large as you have, I'd seriously start thinking about putting in a Salt Water Chlorine Generator. It will release you of the chore of hauling jugs of liquid chlorine home. Did your builder ever mention this option for sanitation?

When buying liquid chlorine make sure you check the production dates. Its like 19283 which translates to the 283rd day of 2019. Which is Today! :kim: You don't want to buy liquid chlorine older than 2ish months, 3 max. I've found some that's weeks old and its *fresh!*

Maddie :flower:
 

dearliza98

Member
Oct 10, 2019
7
Nashville, TN
Thank you for the HDX tip at Home Depot. I bought some liquid chlorine with a date of Sept 23 so that’s pretty good. I’ll be rechecking my CYA and hopefully pouring it in today and will report back.

On the saltwater chlorine generator, we have a steel wall pool with vinyl liner and the pool company would void the lifetime warranty if we went with saltwater due to the steel walls so we stuck with standard chlorine for now.
 

dearliza98

Member
Oct 10, 2019
7
Nashville, TN
So I checked my CYA before I added any liquid chlorine and it was around 50ppm. I added a gallon of chlorine and in two short hours, I went from basically 0 to 3ppm so that’s pretty awesome. I expected a potent smell putting all of that in at once but there’s nothing. No more tabs for me!

Now I need to figure out what this SLAM stuff is and does. I still have a lot of chlorine and non-chlorine shock. Should I scrap that stuff? Thanks for all of the advice.
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
11,536
Evans, Georgia
What a crock of a threat by that pool company!! The reason that's a crock is that in about a year or two your pool will have almost as much salt in it as a pool using a SWG. Each chemical you add to your pool leaves some small amount of residual salt behind. It builds up over time. Almost to the point where when you decide to put a SWG in you won't be adding much more to meet the salt needs.
Makes me wonder if they're aware of that?

Maddie :flower:
 

dearliza98

Member
Oct 10, 2019
7
Nashville, TN
@YippeeSkippy I hear you. They sold me on the chlorine and steel wall package and then said I could switch to saltwater at no extra cost but it would void my lifetime warranty due to the salt damaging the steel walls over time if a leak occurs.

Apparently, if I keep it the way it is, my lifetime warranty covers the entire pool structure (steel walls, floors, etc) for as long as we live at our home. I figured I would keep things as they are for a few years and maybe switch to saltwater down the road.
 

Griswald

Well-known member
Jul 7, 2014
690
Hope Mills, NC
@YippeeSkippy I hear you. They sold me on the chlorine and steel wall package and then said I could switch to saltwater at no extra cost but it would void my lifetime warranty due to the salt damaging the steel walls over time if a leak occurs.

Apparently, if I keep it the way it is, my lifetime warranty covers the entire pool structure (steel walls, floors, etc) for as long as we live at our home. I figured I would keep things as they are for a few years and maybe switch to saltwater down the road.

Wow...are you getting boned!