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.
Can I please get a free online pool book?
Your website is excellent.
Thank you,
Al Machia
New Jersey
MACHIA0705@gmail.com
Signed up and sent. Enjoy!
I have a new above ground 11000 gal pool that will not register a chlorine level. I have tried shocking overnights but nothing is changing. All my other chemical levels are fine but just can’t get chlorine in the pool. Am I missing something?
Mike – I have the same problem. Tried the chat on the website and they pointed me to this post. Doesn’t really help because it does not address the problem.
Are you using tablets or liquid chlorine besides the shock? Shock dissipates pretty quickly as it is supposed to spike the chlorine level not maintain it.
Anyone have a Dive system chlorine generator?…just wondering about your satisfaction of it?
Bump?
I have not heard of their brand, but I looked them up; their cells at least look cool. Who knows if they work or not.
There are so many cool looking products in the pool industry that don’t live up to the hype.
Our pool company closed out pool with out adding the end of season chemicals .. Long story … When we opened it was a murky mess . My hubby has done an amazing job of cleaning .. But our chemical levels are far too low ..
We also had warmer spring followed by excessive rain .. Its getting there but seems like nothing is really happening .. Any suggestions ? tips ?
Thanks … just think we need to add more .. alge was so thick it had texture we still see water bubble and foam up when we add obviously far too many contaminants for pool .
10000gal pool. 8 gallons of liquid shock, 7 packets of dry shock, 25lb of chlorine tablets in pool. Low chlorine and free . half left over half new city water.
What are your latest water chemistry results? Chlorine doesn’t work unless you have the other chemistry levels in check. If you have no CYA, and your pH is off, then you are essentially throwing chlorine down the drain.
check CYA
You are so helpful! Thank you so much. I love your advice…thanks!
My pool chemicals are perfect, the pool is clear as can be, my phosphates are pretty low…… no chlorine reading.
Ok, then you should add chlorine. If your chemistry truly is perfect, all you need to do is add chlorine. I would add a liquid shock dose to give anything lingering in the pool a nice punch; then, I would add tablets, start your salt generator, or whatever method you use to maintain proper FC levels.
what is your intellichlor set to? can you increase the number/amount of chlorine it produces? I have an iChlor 30, I recently had to change it from 30 to 55 for output…….
The I9ntellichlor does allow you to adjust the chlorine output. The required chlorine for a pool will vary according to the size of the pool, the gallon rating of the cell, swimmer load, and time of year. At some point in your season, you will likely need up the output to compensate for higher temps or rainfall.
Just a general question. I want to know the best way to approach the spring opening season to start off with the best and clearest pool water? I know the pool chemistry is the key but I want to make sure of the proper steps to get there. Let me know if I’m following it right.
1. Ph Balance then,
2.Alkalinity then,
3. Stabilizer then once these are right,
4. Chlorine levels (Can you get and maintain chlorine with my Pool Frog system and Super Chlorinating Shock)?
5. After that then Algae Preventer
Am I missing anything? Of course cleaning any debris out before all of this. Thanks!
I have the exact same problem any thing would help thanks.
My pool consistently has low chlorine – between zero and 1.5 in both my home test and the local pools store’s test. I have a Pentair Intellichlor system. The cell is less than 1 year old. I cleaned the salt cell 3 days ago and the cartridge filter 1 week ago. My pool is under a large oak tree, but I run a vacuum and have 2 skimmer baskets which keep both the pool floor and surface very clean of leaves and excess debris. My pool water is a little cloudy but blue and not green – no evidence of algae. I actually had a service tech come out and perform a bucket test to ensure the salt cell is indeed working. My salt level is good, PH is normal, phosphates are low but almost every morning i have to add at least 1 bag of shock to get rid of the stains on the pool floor and also to get the chlorine back up to an acceptable amount. Any thoughts? anyone ever heard of elevated nitrates causing this? if so, how do i address this? Thanks for helping me with this mystery!
If your pool water is cloudy, those are particulates that are soaking up active chlorine. So your cell may be producing chlorine but all that cloudy stuff is eating it up before it can do its job. I would use a clarifier or a flocculant to get rid of the cloudiness. Also, if you are adding shock along with algaecide, that cloudiness may be the result of them not mixing well. Hold off on the algaecide.
I bought a house with a 25,000 gallon salt water pool back in June of this year and it has been a nightmare to deal with. The only time I get a chlorine reading is for the first couple days after I shock the pool. I did have a bad salt cell so I was supplementing chlorine tablets in the skimmer however I never could get a chlorine reading doing that. I have now replaced the salt cell and still have the same issues with it not holding chlorine. PH, Alkalinity and Stabilizer are all in check but no chlorine. Any thoughts?
First, what is the make and model of the salt system? Do you know the pool size (in gallons) the cell is rated for? The cell may be undersized, meaning it can’t keep up with production.
What are your chemistry results? What are the number values?
Wow! You have helped so many people! Thank you very much for that. My question is this.
Why oh why am I getting a chlorine reading of zero ppm?
My pool has a salt reading of 2900 parts per million on three different electronic salt readers. (One on the Hayward and two portable electronic ones.) My pH is 7.5 and my alkalinity is 120 my calcium hardness is 250 and my cyanuric is less than 100 but over 50.
It could be any of the reasons we mentioned in the article. Why your specific pool is struggling with chlorine I cannot pinpoint purely on those numbers as they look on point. But you may want to try to lower the CYA levels. I would try a heavy dose of cal-hypo, pool first-aid (or something similar), and continue with your normal method of chlorination.
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
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.
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.
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?
What is another name for shock
Calcium Hypochlorite.
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??
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
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.
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.
What is the ingredient in the shock you are adding and what percentage?
Have you tried a drain and refill? Instead of throwing shock down the drain, it may be best to start anew.
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?
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
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!
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.
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
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 ?
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.
I have 2 different brand strips and a test kit with the drops.. all reading the same, no chlorine.. should I shock it again?
I have the same problem. Above ground pool. Opened and shocked it. Ran the sand filter for about 25 hours over 2 days. Water cleaned up but was cloudy. Added more fresh water. Tested and saw no chlorine registered. Shocked it again. Water cleared. Tested 3 hours after shocking and all levels tested well. The next morning water is completely clear but still no chlorine. Have backward filter several times. Should I try a oxidizer shock without the chlorine?
Chlorine is not registering the next day because you are adding unstabilized pool shock which dissipates quiclky. In order to maintain a chlorine level, you need to use trichlor, dichlor, or stabilized liquid chlorine. You also need to make sure that your other water water chemistry is blanaced, like the pH, Alkalinity, and CYA.