Step 4
Yet another way to resolve a chlorine lock is to reach what is called breakpoint chlorination. Breakpoint chlorination is the point where the chemical bond that ties nitrogen, chlorine and ammonia together by using large amounts of chlorine. This will cause the chlorine residual to drop rapidly. Reaching a true chlorine breakpoint is vital to breaking a chlorine lock. If breakpoint is not reached using this method, the problem will only get worse. To accomplish a breakpoint, 7.6 free chlorine molecules are used to break apart an individual combined chlorine molecule. The amount of product you will need will vary depending on the type of shock you are using. Aside from knowing your total chlorine, free chlorine, number of gallons in the pool, and the weight of a gallon of water (8.34 lbs.), you will also need to know the type of pool shock you are using. Before attempting this method, the pH needs to be between 7.2-7.4. This equation will be a two part process. The first step will be determining the ppm of chlorine needed to reach breakpoint: (TC-FC) x 10. Using the same amount above, the equation would look like this: (5-3) x 10 = x ppm or 2 x 10 = 20 ppm. I will need 20 ppm of chlorine to reach breakpoint in this 15,000 gallon pool. The next step is to determine how much product I will need. I'm using calcium hypochlorite in this example and need 2 oz. per 10,000 for a 1 ppm increase. I'll need to multiply 2 oz. x (gallons in pool/10,000) x (ppm needed/ppm dosage) which simply put is: 2 oz. x (15,000/10,000) x (20 ppm/1 ppm) or 2 oz x 1.5 x 20= 60 oz. To convert ounces to pounds, I divide by 16: 60 oz./16= 3.75 lbs. So to reach breakpoint in my 15,000 gallon pool I will need 3.75 lbs. of calcium hypochlorite.
Dan K Posted: 5/29/2019
Is it ok to use town water to refill your pool when it is chlorine locked or do I need fresh non-processed water like from a well or lake etc. I wasn't sure if draining and refilling with town (chlorinated) water would fix the problem or make it worse.Reply
Anonymous Posted: 6/5/2019
I just solved the mystery of the chlorine lock in my pool. After 9 days of intensive care and chemical balancing, shocking, and cleaningI was ready to give up. What i did to solve this problem is that i shocked my 10000 gallons with 4 pounds last night, then after 5 hours turned off the pump 12 hours until today after noon no result yet but that i guess was part of the solution. Then today aftrr noon i filled a dry bucket with 6 pounds of shock and dumbed them all togather in the pool instay in the deepest side of ghe pool at the same spot. and right away started brushedthe pool ground andReply
InyoPools Product Specialist Matt S. Posted: 5/30/2019
It is ok to use city water to refill your pool.Reply
Marge Posted: 5/22/2019
How much water would you recommend draining if you are in a Chlorine lock? Our pool is 15,600 gallons?Reply
InyoPools Product Specialist Matt S. Posted: 5/23/2019
Drain a third and refill with fresh water. As step two covers, there isn't a set amount; but if you want to put the odds in your favor, draining more will be better than less.Reply
Sara Posted: 5/21/2019
My pH is 7.4, my stabilizer is low, my free chlorine is .5 and total is 7.5...help!!Reply
Anonymous Posted: 5/23/2019
Yes, I have added 22 gallons of chlorine with no luckReply
Matt S. Posted: 5/24/2019
If 22 gallons of chlorine is not budging it, then you need to drain a third or a little more of your water then refill with freshwater. Your pool is to the point where you just have to press the reset button.Reply
InyoPools Product Specialist Matt S. Posted: 5/23/2019
Have you attempted any of the steps listed in the guide?Reply
Cathy Posted: 5/21/2019
So...we replaced our pool sand with Zeo sand and also replaced our Hayward multi port and laterals. We cannot get our water clear this year!!! It's a hazy light green. You can only see the bottom on the shallow end. We have vacuumed, brushed, backwashed and still don't have clear water. I'm so frustrated!Reply
InyoPools Product Specialist Matt S. Posted: 5/21/2019
Filtering alone is not going to clear algae from your pool; it requires active chlorine. The hazy green is likely a mix of alive and dead algae. I see your list of things you have changed, but have you completed the steps in this guide? You may also want to review this guide: How to Clean a Green Pool?Reply
Jamey Posted: 5/18/2019
I am struggling with my pool this year. Pool is crystal clear but Free and Total Chlorine is at 0. CH is 250, CYA is 75, TA is at 90, PH is 7.4, Copper and Iron is 0, TDS is 500 and Pho is 0. Looking for any advise. I have spent almost $400 so far and cannot get out of this lock. Pool is a 14 x 28 cresent shape with liner that is approx 15,000. Am i stuck with nothing to do but drain ans start over?Reply
InyoPools Product Specialist Matt S. Posted: 5/20/2019
Have you tried everything mentioned in this guide?Reply
Pete Posted: 5/17/2019
Pool is crystal clear but keeps showing 0 free chlorine. Shocking over and over and see algae dying and falling to bottom. FC and TC readings go up about an hour after shocking but flatten back to 0 several hours later. PH is good, stabilizer levels are good. Do I keep shocking? Never had this issue before.Reply
TPorter Posted: 6/18/2019
Did you ever figure this out? Same thing is happening with my pool. It is clear that showing no Coreen and I have lots in itReply
Se Posted: 5/18/2019
I have the exact same problem..I have went through 26 bags of shock with no chlorine readings..I've tested with 4 different kits alsoReply
InyoPools Product Specialist Robert M. Posted: 5/17/2019
Hello Pete - What is your stabilizer level? Is all the algae dead?Reply
Pete Posted: 5/17/2019
Stsbilizer is where it needs to be. Dnt have the ppm handy but it's on the low end of the "good range" I put another bag of TKO in this morningm and more algae was floating up. Water is still clear and that's the perplexing part. ThxReply
InyoPools Product Specialist Robert M. Posted: 5/17/2019
I'd recommend adding more shock until you show a free chlorine level. Start with doubling what you normally put in.Reply
Rob Posted: 5/14/2019
I've been locked before and drained a little more than a third of my pool water. I then ran into hardness of the water issues due to the fact that I have a well. Anyway, I'm not totaly locked at present but the pool is becoming more green by the day and the Ph remains high at 7.8 , the total chlorine 7.8 is high and the free chlorine 2.8 is low. I'm considering trying the second solution and adding 6 pound of the Non chlorine oxidizer. What do you think?Reply
InyoPools Product Specialist Robert M. Posted: 5/14/2019
The best way is to drain and add fresh water but non-chlorine shock has worked for a number of pool owners. The best way to prevent this lock in the future is to keep the stabilizer level under 80 ppm.Reply
Chad Posted: 5/12/2019
I have put so Many chemicals in this pool, and my total chlorine and free chlorine don’t show on the test strips, the pool hasn’t improved and of course is green, is this a sign of chlorine lock?Reply
InyoPools Product Specialist Matt S. Posted: 5/13/2019
Yes, those are exactly the symptoms brought up in the guide.Reply
Anonymous Posted: 5/7/2019
Hello, I have added chlorine powder which raised the total chlorine. The free chlorine is stuck at zero. PH and hardness are perfect. I haven't added any stabilizer. What gives?Reply
InyoPools Product Specialist Matt S. Posted: 5/7/2019
What is your stabilizer level? What is your alkalinity level? Is your pool water clear?Reply
Surika Posted: 12/19/2018
Good day. I have an issue with my pool. (I do not know how many liters or Gallons the pool is) The PH is Balanced, The Alkalinity is balanced, the Acid is balanced, the amount of Back washing is balanced but the Chlorine is non existent. I have shocked the pool,I have added a de flogger, I have vacuumed the pool on waste, I have back washed the pool every second day now and filled up with water and I have added 3kg of chlorine already but nothing comes up on my tester stating that there is chlorine in the pool. We will be replacing the Sand this weekend to see if this will sort out the issue, but the pool is still a misty green blue colour. I cannot keep putting in chlorine into the pool. I have also bought a Stabiliser to see if that would help but I do not just want to put that in the pool and do more harm than good. Please can you help me?Reply
InyoPools Product Specialist Matt S. Posted: 12/19/2018
Hello Surika - To know how much chlorine to put in first we would need to know the pool size in gallons. There are online pool volume calculators that can help with this part. Second, we would need to know the actual number values of your water chemistry; for example, CYA = 80, pH = 7.4, Alkalinity = 100.Also, if your water is bluish-green, then it sounds like you have the beginnings of an algae bloom. Your chlorine is likely being exhausted from trying to combat the algae problem. You need to maintain shock levels in your pool until the green tint goes away. Read: How to Clean a Green Pool?. But again, to know the necessary shock levels for your pool, you need to know the pool size and water chemistry values.Reply
Anonymous Posted: 12/20/2018
Thanks for the reply. I Vacuumed the swimming pool last night to get rid of the dust at the bottom, drained quite a bit of water and refilled (Will fill up to full capacity this afternoon). The swimming pool looks much better this morning. We will also replace the sand this weekend and I think then we will be ready to go. What I can tell you is that the pool is 1.3 meters deep, 6 meters in length and 4 meters in width. I will check if the pool goes green and add a Algae remover. Thanks againReply
Inyopools Posted: 5/17/2018
Hello Blinded - The method of adding more chlorine to break chlorine lock sounds weird but it does work. There is no easy method but draining and refilling is the route that I usually recommend.Reply
Blinded Posted: 5/15/2018
I am just jammed up on this Chlorine issue. I have a 62,500 gallon pool. ph is 7.5 free Chlorine is .9 and total is 9.8 Hardness is 342 Alk is 241 They told me to put 68 pounds of Calcium Hydrochlorite in. I am just baffled. They keep saying the pool will break. So why put more chlorine in. I double shocked it. Going to hope something changes. I need devine help. BlindedReply
InyoPools Product Specialist Dennis R. Posted: 8/29/2017
Jimmymag - It sounds like you are at the point where you have to replace 18" to 24" of your water. If your nitrates are high that could be causing what appears to be chlorine lock. See "Anonymous" posted on 5/31 for a similar problem and solution.Reply
Jimmymag Posted: 8/27/2017
I have a problem similar to the one that Ray posted on 8/23/17. I have 26,500 gal. plaster lined pool. I have been using liquid sodium hypochlorite (10%) which I had to add a gallon every couple of days to keep the level above 2ppm. The ph gradually increased to 7.8. I added some muriatic acid to bring the ph down a little. After doing this, a problem developed with the chlorine. The FC level dropped to zero. To shock, I added 2 gallons and checked the FC after a couple of hours and it was about a three so, I added 2 more gallons late in the day Over night the FC reading was zero. I went to pool supply to have water tested. They said the the cyuratic acid level had dropped to zero. They recommend using 5 lb. of di-chlor to superchlorinate. I did this and the previously clear water turned cloudy like Ray’s did. I ran the pump for about 16 hours but the water was the same. I added some old clarifier that I had and that cleared the water. I superchlorinated with the liquid and again the FC dropped to zero in 12 hours (overnight) . Pool supply recommend something they call “Purge” . Added that and ran pump for 24 hrs and thoroughly cleaned filter. I had water tested and ph still 7.4 and cy acid and all other tested good. I superchlorinated with liquid and again overnight the FC was zero and the water is sparkling clear with no signs of algae. Pool supply retested and all readings were good except that phosphates were 300. They had no answer to the chlorine problem. I shocked again with the same result. Back to pool supply and they ran an additional test for nitrates. Nitrates were high and they said there is no chemical treatment for nitrates and that replacing some of the water was the only way to lower nitrates. There is no chlorine odor My question for you is… could the nitrates be causing the chlorine problem? Thanks, JimReply
InyoPools Product Specialist Dennis R. Posted: 8/25/2017
Ray - What is your stabilizer level. If it's 0-20, you will have to add more to protect the chlorine from being burned away by the sun. If it's at the 100 level, you may have too much stabilizer in the pool which locks up the chlorine and gives you a 0 reading. The only way to reduce stabilizer is by draining a foot or so of the pool's water.Reply
Ray Posted: 8/23/2017
I have a 33,000 gallon in ground plaster pool. I actually have a 2 part question. My first question is regarding chlorine. For some reason my pool zeros out on chlorine weekly. I am not sure why. All my test readings always come back fine except the chlorine. Any knowledge on why that is? My 2nd question is regarding cloudy water. My pool was fine a week ago and then out of nowhere my pool looks like a milky white. I can see the bottom in the shallow end of the pool, but cannot see the bottom in the deep end. I tried non-chlorine shock, water clarifier and ran the filter for 24 hours during this process. Nothing changed. Any other ideas would be great. Thank you very much.Reply
InyoPools Product Specialist Dennis R. Posted: 8/15/2017
jjcresci - I'm not sure I have enough information to know what your problem is. If you have drained a significant amount of your pool water, like 1/3, you shouldn't have chlorine lock - if you even did. Your chemical numbers like ok except for your FC. How long have you had no chlorine in your pool? If it's more than a couple of days, your pool should have become cloudy by now. Did your chemical readings come from a local pool store? If not, I would have them check your FC. The function of non-chlorine shock is to oxidize chlorine. If you have no FC, I'd question its use. If your pool is starting to cloud over, I'd add a couple of bags of regular shock to see if that brings your FC up and clears your pool.Reply
jjcresci Posted: 8/13/2017
my pool was fine until my timer went.had to be off 4-5 days .I replaced timer. My pool was cloudy. So i got it running within 48 hrs it was clear. now pool has 0 fc.about 10,000 gallons
ph 7.6
Alk 130
stabilizer 80 always been 80
calcium 200
this is a vinyl liner pool that is crystal clear ,but 0 fc will not hold FC and no alge at all
any ideas i did drain water and i'm thinking of useing non chlorine shock.
Help
Reply
InyoPools Product Specialist Dennis R. Posted: 7/25/2017
Jennhurley59 - Not sure what is going on here. "Chlorine lock" means that the chlorine in your pool is ineffective - cannot eliminate algae. Even if you were able to break the chlorine lock without adding chlorine, I don't know how you avoided growing algae without adding chlorine for two months. If you are now seeing algae growth, I would shock the pool and begin adding regular levels of chlorine plus add whatever chemicals you need to balance the pool.Reply
Jennhurley59 Posted: 7/24/2017
My pool had "chlorine lock", cya levels through the roof we drained and refilled for weeks. Along with adding no chemicals, no algae grew for over 2 months. Now pool is finally turning green, is this a good thing?Reply
InyoPools Product Specialist Dennis R. Posted: 7/13/2017
Lifetimelinda - I'd check your CYA reading again. Adding more CYA to your pool if it has a 100+ reading is going the wrong way. Too much CYA can lead to chemical lock. I'd lean more towards draining 20% or your pool (generally 12' to 18") then adding non-chlorine shock (step 2). See "Anonymous" comment 4 comments down.Reply
Lifetimelinda Posted: 7/11/2017
The pool store is saying I have a chemical lock. My readings were chlorine 3, ph below 7, phosphate 1000 and cynaric acid 100++. They suggested I drain 3/4 of my pool and start over. Went for second opinion and they said I had no stabilizer,start with getting it up, then work on alkalinity and then ph. We are pool newbies. So confused so starting with the stabilizer. We have small pool, just 12000 gal. Any thoughts.Reply