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Why Does My Pool Have No Chlorine?

Have you ever tested your swimming pool water and couldn’t get a chlorine reading? Figuring you must have done something wrong, you retest your water. Still no reading. So what do you do? Add chlorine, right? After days of adding chlorine and testing chemical levels, you still have no chlorine reading. At this point, your attitude turns from curious to annoyed.

Are your chemical levels imbalanced?

Are you using a reliable pool water test kit?

These are just two questions that need addressing before you can get to the real question, why does my pool have no chlorine? 

Determining Why My Pool Has No Chlorine Reading

Balance Your Pool Water

Excluding chlorine, are the remaining chemicals in your pool balanced? Balancing your water is an important step that pool owners sometimes forget. The very first thing you want to do is get an accurate reading of your chemical levels.

If you don’t have a home testing kit, we recommend either purchasing one or taking a water sample to a local pool store and testing it there. Getting the most recent and the most accurate chemical readings is imperative before adding any additional chemicals.

 

High Chlorine Demand: What Is It and How Is It Caused?

If you test your pool water and can’t get a chlorine reading, it may be due to your pool’s high demand for chlorine. A high chlorine demand (sometimes referred as chlorine lock), simply means that although your water may appear clear and balanced, the chlorine in your pool is ineffective. But why?

If you need guidance on balancing your pool, check out our blog here.

Too Much Organic Material In Your Pool

One of the causes of a high chlorine demand is an excessive buildup of algae and phosphates. Although you’re adding chlorine to your water, bacteria or algae are overpowering the chemicals causing it not to show up on tests strips or in water kits.

It’s like when you overdraft $200 from your bank account but only add $100 back. You’re still less $100 from the original overdraft. The chlorine in your pool acts the same way.

Keep in mind, organic materials like algae, leaves, sunscreen, lotions, pee, poop, and etc., consume chlorine. As chlorine does its job, it is depleted in the process. To prevent the demand for chlorine from happening, help remove the organic material from your pool water by brushing the algae from the pool walls, cleaning your filter, and removing leaves and debris from the water.

Chemical Imbalances

One of the ways phosphates get into your pool is through household cleaners. There are certain household cleaners that weren’t designed for the pool. Cleaner manufacturers add additional components to the composition such as phosphates or nitrates. The extra phosphates interfere with the pool’s current sanitizer and can cause a demand for chlorine.

Having too much cyanuric acid in your pool is another way to create a high demand for chlorine. Sometimes, it’s just a simple case of pool owners adding too much stabilizer to the water. Sometimes this occurs when you aren’t partially draining and refilling your pool periodically.

Adversely, very little or zero stabilizer also creates a demand for chlorine. Cyanuric acid, in a sense, acts like sunscreen for the pool. If you’ve ever worn sunscreen in the hot sun, you know that you have to consistently re-apply. Our pools are the same way. If your CYA levels are really low, the sun can burn through the chlorine in your pool rather quickly.

You can learn more about the relationship between chlorine and cyanuric acid here.

Rainstorms or Excessive Rain

Other ways that can potentially cause a chlorine demand in your pool is excessive rain. When it rains, air pockets form in the raindrops and allows oxygen into the water. When this happens, your pool’s chemistry offsets, resulting in the demand for chlorine.

 

Determining If Your Pool Has a High Demand For Chlorine

The quickest way to determine if your pool is experiencing a high demand for chlorine is to perform a test for free and total chlorine.

Free chlorine shows the level of disinfecting chlorine available to sanitize your pool. Free chlorine isn’t interacting with contaminants, yet. Total chlorine is the amount of chlorine, used or not, in your water.

In the test, if your free chlorine reading matches your total chlorine reading, your pool is NOT experiencing a high demand for chlorine. This is a normal reading.

However, if your free chlorine reading is different than your total chlorine reading, then there’s a problem. You shouldn’t have a free chlorine reading of 3 and a total chlorine reading of 7.

 

Breaking Your Chlorine Lock

While there are many ways to solve this issue, we will only be covering a few of them. Please select the option you are most comfortable with.

Partially Draining Your Pool

One of the simplest methods to breaking chlorine demand is by partially draining your pool. The severity of the chlorine lock determines how long this method takes. Unfortunately, there’s no exact science to this. Simply drain your pool little by little, refill it, test it, and repeat if necessary.

Shock Your Pool

Another method of breaking chlorine lock is shocking your pool. Bring your chlorine levels to 20ppm or three times higher than the current levels. We recommend using a non-chlorine oxidizing shock until your free and total chlorine reads the same.

We typically see more pools with a high demand for chlorine during spring opening season. A lot of the times, pools sit for months accumulating a ton of different contaminants. This is one of the reasons we always recommend balancing your pool before you close it. You don’t want to compile pool issues or push them to the side. Although high chlorine demand is more common than you might suspect, it is something pool owners can handle themselves.

Give us a call if you think your pool is experiencing this same issue. Make sure you have your most recent chemical readings before we can offer any help.

74 thoughts on “Why Does My Pool Have No Chlorine?

      1. My pool water is green but clear. I filled the pool with hose water from our town supply and right fr the time it was filled it looked yellowish or light green. I shocked the pool and ran the pump overnight and the water is crystal clear but still tinted green. There is sediment on the bottom of the pool now. I also used stain prevent and ran the pump overnight and the colour has not changed at all. Wondering what to do.

    1. I have a saltwater pool, and the free chlorine level has been at zero. We’ve added salt to it and ran the pump and have shocked it. We opened it up middle to the end of May. Vacuumed it a few times, haven’t been able to get in yet because we’ve been having a lot of rain and storms this spring where we live, pretty much everyday in May and a few times so far this month. Our pool is not blue but it’s clear and has a greenish look to it. Could it be because of all the rain and that we need to scrub this sides to get rid of the algae?

  1. Could a filter that needs to be replaced cause the chlorinator to always have a red light for water flow and thus not make any chlorine? We have cleaned the cell and the filter and the problem persists.

    1. The issue could be two things, Either the cell needs replacing or the filter is so dirty it is restricting flow much the generator cannot turn on.

      To determine if your filter is the problem, bypass the filter media. For cartridge filters, remove the cartridges and the manifolds. If you have a sand or a DE filter, set your multiport valve to recirculate. If your salt generator still says low flow, then chances are it is not a filter problem.

      1. We are total pool novices-so are you saying to literally take the filter out and then start the pump without it and see if it gets flow to the chlorinator?

        1. I am saying to bypass the filter media (aka the sand, cartridges, or DE grids) by either using the recirculate feature on the valve or removing the cartridge inside the filter. This means your water should have a straight shot through your system with little resistance. What kind of filter do you have?

          1. We have a Pentair filter R173216. yesterday the chlorinator ran just fine. Today the lights flash between red/green on the salt and no water flow which is what it started doing last week. We’ll take the filter cartridge out and try it as you suggested and order a new filter just in case. Hopefully it is the filter and not the chlorinator. Appreciate your advice!

  2. Help please. Definitely experiencing chlorine block. All other levels are in line – phosphates a little high at 844.
    I was told to shock and retest. I did and the bromine level came up but the pool never cleared (its very cloudy) – I waited a couple days, retested – NO bromine level again.

  3. We had a lot of pollen enter our pool (the crew that opened it in the spring just swept the pollen that was on the cover into the water as they removed the cover). This resulted in a very high CYA reading (>100). We drained about 16 in of water from the pool (capacity 29,160 gal). The readings at that time were:
    FAC/Bromine: 0.5
    ph: 7.2
    Total Alkalinity: 60-120
    Total Hardness: 200-500
    CYA: >100
    After refilling, the CYA is around 40, and I have added 12 gallons of Liquid Shock (sodium hypochlorite) but the FAC levels do not seem to have risen. Should I just keep adding shock? Is granular better? I was avoiding using granular sodium Dichloro-s-triazinetrione dihydrate because I was afraid it would introduce cyanuric acid, which we just lowered.
    Thanks

  4. Hi there! I feel like I’m needing a lot of help. We opened our above ground 30 foot pool a couple weeks ago (cartridge filter) and have yet to get it clear. We were fighting iron and it always stayed cloudy blue never brown. This of course made it impossible to get a chlorine reading. This past Friday our pump broke as the temps soared to mid 90s! The water turned to a green color now. We have been using our robot sweeper constantly to sweep up anything and don’t have any algae on the floor anymore. Our new pump is finally running and upon testing everything, here are the results:
    Total Bromine: 0
    Free Chlorine: 0
    pH: 6.8-7.2
    Total Alkalinity: 80-125

    What are the next steps we need to take to get our pool crystal clear?

    Thank you so much!!

      1. So raising the pH first by borax and then working on the chlorine how? I always thought we had to lower the pH first and then super shock to get a chlorine level??

  5. I just added 4 gallons of shock to my 16000 gallon pool and the strips show no chlorine. Should I add more shock?

  6. I am having a problem with my pool and have yet been able to swim in it this summer. I have taken it to our local pool store to have the water tested and it shows all levels normal except no chlorine every time. I’ve dumped algacide and shock in it repeatedly and still green with no chlorine. It now is having the shock floating on top and won’t even dissolve. The pool place is stumped with no more suggestions.

  7. Help!!! Everytime I test my pool, it shows no chlorine. However all other results are within range.
    Bromine 0
    FAC 0
    Alkaline 80-120
    Ph 7.2-7.8
    The pool is clear, so why am I not getting a fac reading?

    1. I’m pretty sure this is covered in the article, but I digress.

      What is your CYA Level? Also, have you taken your water to a pool store for a free water test? The in-store tests will give you more accurate test results than your average strips.

  8. I have in ground pool 16×32 I have the PH at 7.6-7.8 I have zero reading on Chlorine No matter how much I add the water is clear but with a green tint very puzzling never had this issue please help

    1. Ok, p is only one of the important balancer chemicals needed to ensure your chlorine is able to work efficiently. What are your total alkalinity, CYA, and phosphate levels? Give that section in the article a reread for an in-depth explainer on why they are important.

  9. Hello! My above ground intex pool is a little cloudy. The test strips read:

    Bromine- 0
    Alkalinity – 80
    PH – 7.8
    Total hardness – 0

    Any ideas what to do? Yesterday i ran the hose for 40 mins to add a bit of water (as the pool is only about half full anyhow for kids safety) and then did a shock treatment and let filter run for 24hrs. The ph and alkaline went up a little in normal ranges but i still have a reading of 0 for bromine and hardness. Im just wondering how safe this is for swimming and what else i can do to increase those levels. Thank you in advance!

  10. My case.
    We put in the pool 2 , 40 lb bags of salt. Then now, a get chlorin zero.
    OK I put in there phosphate remover, water get cloudy and again chlorin zero.
    I put in bottle ! gallon of chlorin, and i minutes again zero chlor.
    OK, chlorinator is working, so I ordered company to drain pool completely and acid wash surface of pool.

    Waiting for results. I belive, my sanitizer iChlor 30 is in very good shape. Almost new.
    From Florida, Thyronx

  11. next week I’ll leave here comment how my pool is it?
    There is clear signs, then water in the pool is not good.
    Otherwise>
    Water is balanced, 7.8 pH bit high ,
    Calcium Hardness 500 little high,
    level of salt 3,500,
    Total alkalinity 120,
    Total disolved Solids 5,000 high,
    Stabilizer 100, high,
    Chlorin 0

  12. Inground pool at a hotel so used on a commercial scale total is 24000 gallons
    PH 7.2
    CYA-0
    Alkalinity-60
    No chlorine shows up on tests
    added 2 gallons of chlorine yesterday

  13. just opening pool for the summer. have tried to maintain it through the winter. temperature rise, rainfall, pollen, and all that have left me with nothing showing on a test strip. should I start by trying to adjust ph. don’t want to keep throwing good shock after bad.

  14. My test strips (2 different bottles, 1 being brand new) show 0 chlorine. Water tested at store today showed chlorine at 10. Dipped one strip near jet to see if that made difference. Still 0. Help, I don’t want to have to run to pool store every other day.

  15. Help!!! We are opening our pool and got stuck with a very light real green pool. We have added over 16 pounds of ph and it still will not move from below 6.8! Chlorine will not stay in the pool. We have been aerating for over 8 hrs and still the ph will not raise. What are we doing wrong??

      1. Is the pH increaser completely dissolved into the water? Some times the powder just sort of floats around without properly mixing in the pool water. If you have adjustable return jets, adjust them, so they are pointing towards the surface of the pool to churn it better. If you have a waterfall, deck jets or any other water features that agitate the water, turn those on as well. Give it a day or so and retest.

  16. I am having a chlorine lock issue. I did the non chlorine shock that the store rep told me to do and still no chlorine reading. My pool is crystal clear, just no chlorine.

  17. Hey I am after some help I have been treating my pool with shock after it was it used over winter my water appears clear but when you look into the pool it is cloudy I have done a test and it looks to me like everything is okay could you tell me why it is cloudy and what I need to do?

  18. I opened my 20,000 gallon in ground pool and have pH at 7.3 and alkalinity at 90 but chlorine reads 0 despite a fully open inline chlorinator and six gallons of liquid chlotine. Pool was heavily green at opening since getting chemistry to levels above and 12 bags of shock over 4 days pool remains hazy turquoise green. Any advice anout what to do next? Keep shocking it? Hire a witch doctor???

  19. I am at the point of adding dynamite to my pool! All my levels are perfect except my free chlorine. First thing I did was add flock and vacuumed on waste, refilled pool. Did this three times. Then brought my PH to 7.2. Had water tested at pool store, got everything balanced but my free chlorine is still not registering. Even after adding all the fresh water. Should I oxidize it being that it is well water or go the the fort fix and get dynamite?

  20. Help it has been over a week of opening inground 17K gallon pool. Pool Store said we have chlorine lock. Per store recommendation we have added 27 bags of Bioguard Burnout and still no reading on Chlorine. Prior to the 27 bags of burnout we drained down the pool about 3 feet and added fresh water. The numbers from the test saying we had chlorine block were:
    PH 8.2 Free Chlorine 0.5 Total Alkanlinity 289 Total Chlorine 8 CYA 38 TSA 300 and Optimizer Plus 28
    Hardness 96 Also said Combined Chlorine 7.5
    We have a DE fliter and have backwashed numerous times at 20lbs torn apart the filter washed down the fins and started all over again. 2 times a day and still no luck. Thoughts, suggestions, please help. Thanks.

  21. Hi, I have an above ground pool 24ft. I too cannot get any thing on the rear strip. Took a sample to one pool store, they said to drain the pool 6inches below the skimmer and fill back up and repeat this process 5 times. Another pool dealer sold me a kit, we had to put a gallon of chlorine in the pool and then put this powder in the pool and then mix this other stuff with 5 gallons of warm water and let it sit for 4 hours then our into skimmer and run for 4 hours. They said we had too much conditioner in the pool. I haven’t even added conditioner in the pool this year yet. Do you know what our problem might be.? We also have a big dark spot on the liner on the bottom of the pool. Please help.

  22. Have a 1,338 gallon in ground plaster pool. Every time I add chlorine it’s gone within a few hours. Last water test results:
    FAC – 0
    TAC – 0
    CH – 200
    CYA – 150
    TA – 80
    pH – 7.4

  23. I have a 10,000 gallon above ground pool with a sand filter. I can’t get chlorine to register and I’ve put in 6 gallons in the last 2 weeks. We’ve had really bad rain the last few weeks so I drained out as much as we could and added fresh water yesterday. I have been brushing and vacuuming for a week and the water is now blue and very lightly cloudy. My pump for the last week has been running 12-15 hours a day especially at night when we put in whatever chemicals that were needed.

    My test strip readings from this morning :
    – No Chlorine
    – PH: 7.2
    – Alkalinity: 180-240
    – Hardness: 100
    – CYA: 40

    I’m not which of these I need to raise/lower first before I will start to get a chlorine reading.

  24. I shocked my pool with a gallon of liquid shock waited 24 hours tested the water, no chlorine. Added 2 chlorine tablets into the floater tested the next day with a strip, no chlorine. My alkalinity is low, but the ph is okay. My free chlorine matches my total chlorine and that’s zero. My pool is crystal clear, what should I do ?

    1. I would get my water tested by a local pool store. Those test strips can get fouled easily, making their readings worthless. Get the water tested to verify the strips are correct. You may end just needing to buy a new set of test strips.

      1. I have 2 different brand strips and a test kit with the drops.. all reading the same, no chlorine.. should I shock it again?

  25. I have a 24,000 gallon pool. I was out of town on work and it ran out of chlorine in the chlorinator. Shocked the pool and it it now clear as can be. Turned chlorinator all the way up but I am still getting no free chlorine in my test strips. Pool store ran my water. FAC .3 TAC .7 CC .4 PH 7.3 Hard 160 ALK 79 CYA 34 Copper .2 Iron .1. they told me to add 3 gallons liquid chlorine. After doing this my test strips still show no FAC . Any advice. Thanks

  26. Free chlorine does not go up! I’ve been struggling with my pool this year. We open the pool about 45 days ago (15,000 gallons), and added about 20 gallons of liquid chlorine and about 15 pounds of granular chlorine (super shock), but there is basically no free chlorine in the pool. PH, alkalinity, and CYA are within normal ranges. Last week, I treated for phosphates, but still no change in free chlorine. I’ve also replaced about 1/3 of the water in the pool. I have an in-ground pool with an automatic cover, so the pool stays covered for most of the day. Any help will be appreciated. I replaced the filters this year, before opening the pool.

  27. I just barely finished filling up our above ground pool. 18×20 and I already added 3 gallons of chlorine and still get no reading of it added. Help!

  28. All my pool chemicals are balanced. I shock the pool and my free and total chlorine appear on my reading to be the same. After a few hours my pool reads 0 for both chlorine levels. What do I do?

    1. Shock can dissipate quickly depending on the state of the water and time of day. Chlorine can get burned off on hot sunny days. The most common type of shock Cal-hypo should generally only be used in the evening for maximum effect. If you are using the shock in the evening and it is still getting gobbled up then you need to shock it again. The chlorine is disappearing because it is being used to fight something in the water. You may also have some organic material using the chlorine, so a product like Pool First Aid

  29. no chlorine reading here either countless bags of shock 20,000 in ground pool saw some pink slime seems to be gone not used alge stuff ph and alk seem to be in order……….dont know what to do added 4 bags of shock this morning pool still cloudy very little reading.

  30. I have a hot tub, and during the hot weather I set the temp to 30. its always been fine. I have the strips, have a high PH so have to lower it a lot… then, all of a sudden. The PH shows the same (low) but regardless how much Chlorine I put in, the strip says it has NONE! it doesn’t change colour at all. The water is now a bit cloudy… should I just part drain it as it says up top?…Should I think about using one of those floating dispensers instead of keep putting granules in every few days?

    Any help greatly recieved

    yours
    Frustrated
    Essex
    England

    1. Because it is a hot tub, I would consider just purging, draining and refilling it. Starting fresh will be a lot easier than racking your brain over a small body of water. Also, if your water has been in there for longer than a few months, it gets harder and harder to manage because it has been treated so much.

  31. I’m so frustrated, I cannot get chlorine level. I followed your formula for breaking Chlorine lock, which came out with putting in 15lbs of shock. The next morning I got these readings:
    Ph: 7.4
    Alkalinity: 120
    CYA: 220
    Hardness: 30
    FC: 0
    TC: 1
    I have tried everything. When I closed it last year everything was balanced. It does have a slow leak so by the time I opened it, mid-June, I had to refill it from half way. The pool is above ground 24 ft Round x 5 ft deep approx. 13,500 gallons. Suggestions??

  32. My husband set up our above ground pool while I was away and he forgot to add chlorine tablets into the floating dispenser. It was set up for four days with no chlorine and the kids playing in it. I filled the floater with chlorine tablets yesterday- but for some stupid reason I diddnt use as much as I should have…. about half as much actually.
    I tested it today and the PH is higher than 8.4. Total chlorine is reading 0 and free chlorine is at 1. Stabilizer is also reading 0. My thought is that the pH is so high because it didn’t have chlorine for four days. Will adjusting the chlorine levels With a trichlor product help lower the PH?
    How can I fix this?

  33. I bought an above ground pool with a pump and salt water chlorinator. I filled the pool with water from the hose(our town supply). The water was between light green to yellowish tinted but not cloudy. I shocked the pool and the next day the water was crystal clear and you could see right to the bottom but it was still tinted green. I read that it could be a metal problem so I put stain prevent in the pool water and ran the pump all night but the water colour hasn’t changed. It is still tinted light green. There is dark brown sediment in little piles all over the pool floor now. Wondering what to do from here.

  34. Please help! My pool is very green & cloudy. When we took a cup of water to the nearest pool place, they said the water appeared very clean in the cup. I’m not sure how to get rid of the green, cloudiness because I have already added chlorine in it yesterday. It appears a little bit better today, but not by much. Here are my #s:
    Alkalinity: 53
    pH: 8
    Stabilizer: 24
    Hardness: 52
    Free chlorine or combined chlorine: 0

    1. First, all of your water chemistry is out of whack. You could throw a bunch of chlorine in there but it isn’t going to do much because your water chemistry lessens its effectiveness. You need to lower your pH, raise your stabilizer, alkalinity, and hardness. Read and follow the steps of this guide: How to Clean a Green Pool?

      Also, if the person at the counter didn’t tell you the stuff above when they gave you the results of the test, never go back to that store.

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