Chlorine level won't rise after shocking

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bennettair193

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Aug 7, 2013
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Hi. My pool has been eating through chlorine for the past month and I'm not sure what might be causing the issue.

Here are my pool specs:
size: 20x40 8.5 ft deep inground pool. 35000 gallons
filter: hayward sand filter
heater: hayward
automatic chlorinator
UV filtration unit
Avg Temp: 90 degrees

Since we keep the pool temperature high, I expect to run through chlorine faster, but this is almost instantly and it is a problem that has just occurred over the past month. I don't see any signs of algae and the last test we brought to the pool store didn't show algae was present. The UV system prevents most of this, so I woul be surprised if get bacteria.

We haven't been able to get the chlorine level high enough to superchlorinate with Lithium shock granules, so yesterday we purchased 8 gallons of liquid shock and put that in the pool. Around midnight, I added the final 4 gallons and 45 minutes later the reading using my taylor test kit was above the 5ppm limit on the test. By this morning, by FC was back down to .5 with a CC of 1.0. I have my chlorinator set to 4ppm, so it's eating through tabs, but never getting the FC high enough to get a reading.

The PH and Alkalinity won't budge either. PH is steady at 7.2 and alkalinity is holding at 180

My CYA is a bit high at 80

I have read that it might be ammonia in the water, but I don't have a way to test, and I would have though the liquid shock would have caused an increase to the CC reading as it bonded with the ammonia, but it hasn't changed.

Any help would be appreciated
 
Welcome to the forum :wave:

Your new best friend, other than all of us, is Pool School. Your pool will be cured with the SLAM process.

Having 80 CYA makes your shock FC level around 21 to 31.

Adding 4 gallons of (guessing) 10% bleach/liquid chlorine will add about 11 ppm FC. So, you are way under shock level.

Have you found the PoolCalculator yet?

I suggest you replace some water and lower the CYA to about 50 and then start the SLAM process outlined in Pool School.

It will be helpful if you post a full set of test results and tell us how you got them.

Also, adding a sig with pool and equipment specs will be nice.

Don't forget a pic! :-D
 
btw, stop using tabs. They are adding to the CYA problem.

If you want to test for ammonia you can buy a test kit at a pet shop, wallyworld, etc for about $15. Some pet stores will do a free ammonia test.

Your problem sounds more like regular ole organics consuming the chlorine. With ammonia, we usually see higher CC.
 
Welcome to TFP.

Which test kit do you have? At very least you need to add the FAS-DPD test to it.

Start by reading the ABC's of Pool Chemistry in pool school.

The CC of 1 ppm says that you need to SLAM your pool. There's a link in my sig on how to "properly" do that. 8 gallons of 10% would have only raised the FC by 23 ppm which isn't even SLAM level for 80 ppm CYA.
 
Hi, welcome to TFP! You can go to a pet store and get an inexpensive test for ammonia in the fish supplies section, but I don't think ammonia is your problem since you are getting a CYA reading.

Bottom line is you have something in your pool that is consuming the chlorine. It may be a nascent algae bloom. What does the water look like? Is it crystal clear or cloudy? Is this an indoor or outdoor pool?

Your UV system won't prevent bacteria from invading your pool. The water treated by the UV is only sanitized while it is in the chamber. Once it mixes back into the bulk pool water it is contaminated again. The UV system cannot sterilize enough water quickly enough to prevent re-contamination if a pathogen is present. Usually the only time a UV unit is effective is for an indoor pool with no sun exposure, and then it is only effective for burning off combined chloramines, not for sanitation.

One of the best investments you can make in your pool is a high quality FAS/DPD test kit such as a Taylor K2006 or a TF 100. An FAS/DPD test kit will allow you to test chlorine values high enough to superchlorinate (what we call the SLAM process) your pool. By plugging your test results into the Pool calculator, it shows your FC target to be 21 ppm to complete the SLAM process. That means you must bring the FC to 21 ppm and keep it there by frequently re-testing the FC and adding more chlorine to keep it at the target level until the process is complete.

You can read more about the the slam process and overnight test for more information.
 
The problem is that your pool is overstabilized. You're using trichlor pucks in that automatic chlorinator, correct? Every 10 ppm FC you add via pucks also adds 6 PPM CYA. So the first answer to your problem is no more pucks.

Second, to keep the algae at bay - not kill it off, just keep it from starting requires a minimum FC level of 6, all the time. If it dips below that for any length of time, you'll likely get algae, and as stated above, to kill it off faster than it can reproduce requires 31 PPM FC for several days. Perhaps weeks. Certainly more than ten minutes or so that a one-time "shock" provides. pool-school/chlorine_cya_chart_shock

You have a huge pool, so it's going to take a lot of bleach/liquid shock. Same stuff, different concentrations. It will be easier to SLAM the pool if the CYA is lowered. And that, unfortunately means draining about half the water and replacing it.

You have most of a proper test kit... need the FAS-DPD powder test that can measure as high as 50. Luckily, that part is available separately here.
 
Thanks for the information. After posting this I took water samples to two different pool stores and they ran it through the computer. Both came up with similar readings which are different than my Taylor Test kit, so it changes the dynamics a bit.

Here is what the computer came up with:

PH: 6.7
Alkalinity: 114
FC: 0
CC: 0
CYA: 57
No Algae is present

The stabilizer is lower than my test kit reading, so I may have done something wrong.

Does this change anyone's thoughts or should I go ahead and SLAM it as first suggested?
 
I would definitely trust your readings more than the pool store's. You can add the FAS-DPD test to it and have a pretty good test kit.

Go ahead and start the SLAM process, but you'll need the FAS-DPD test to perform it correctly.
 

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Okay, here is where I am.
I SLAMMED the pool last week, keeping the level at 25ppm. It stabilized overnight and maintained normal chlorine levels for about 3 days.
Do to some issues with skin irritation, we converted to a SWG from Hayward 3 days ago. At the time I discussed the chlorine consumption issue with him and he checked for phosphates. We had a reading of 500, so we put Phosfree in and now the reading is 0.
We just got the salt level up to normal today, so I had added 4 bags of lithium shock to the pool, just to maintain the chlorine while we were adjusting the salt level.
I added the lithium shock at 11pm and this morning the FC reading was back to 0 and the total chlorine is .5
I wouldn't think that there would be anything still alive to eat the chlorine after SLAMMING it, but it still won't hold chlorine. The pool is crystal clear and there is no evidence of algae, such has slick surfaces. Does anyone have any suggestions at this point?

CYA level is 57
FC - 0
TC - .5
PH - 7.5
TA - 114

water temp is 88 degrees
 
[s:1uojthme]Lithium is not chlorine and quickly goes away[/s:1uojthme]. You need to get some chlorine in your pool.

I know you didn't ask, but phosphates are irrelevant.

Read "The ABC's of Pool Water Chemistry" up in Pool School.....there's a ton of info there that should help you. It will also probably prompt a lot of questions so ask away. :-D
Does anyone have any suggestions at this point?
Click to expand...
Stay out of the pool store, you are being given a lot of misinformation.
 
I understand the situation with the phosphates, but I also know that they are food for algae and if I have algae, I wanted to go ahead and make sure that was removed before spending time shocking the pool. I started with liquid chlorine and added 8 gallons and it was gone the next day also.

Since the pool salt level is in balance, I have gone ahead and manually added 4 gallons of liquid chlorine and then turned up the SWG to 80% to get the chlorine going. I'll see what we get tomorrow.
 
Sounds like you got impatient, did not follow the SLAM process to completion, then got bad advice from the pool store that cost you a lot of unnecessary money.

You have to pick them or us. You can not mix the advice.
 
duraleigh said:
Lithium is not chlorine and quickly goes away. You need to get some chlorine in your pool.
Click to expand...
I am in error above. Lithium Hypochlorite is indeed chlorine......sorry for the misinformation and my lack of paying attention.
Click to expand...

But it is the most expensive form of chlorine with no added benefit and certainly a waste of money.
 
That's okay. I only used the lithium after accidentally using a cheaper version of the granular shock and I'm still cleaning up residue at the bottom of the pool from that junk. Every time anyone swims it clouds up my pool and the vacuum just moves it around instead of actually sucking it up. I put the liquid chlorine in about 2 hours ago and my FC level is at 2.5. Hopefully, with the SWG up to 80% I can keep the chlorine level stable.
 
bennettair193 said:
That's okay. I only used the lithium after accidentally using a cheaper version of the granular shock and I'm still cleaning up residue at the bottom of the pool from that junk. Every time anyone swims it clouds up my pool and the vacuum just moves it around instead of actually sucking it up. I put the liquid chlorine in about 2 hours ago and my FC level is at 2.5. Hopefully, with the SWG up to 80% I can keep the chlorine level stable.
Click to expand...

I'm considering an SWG so I'm going to ask a question that is as much for my benefit as yours. I don't understand your logic in only adding enough liquid chlorine to bring your FC to 2.5. Wouldn't you benefit more by bringing your FC up to 7 or so with the liquid and letting the SWG hold it there?

The FC goes up quicker that way and it's easier on your SWG. A FC of 2.5 is way too low for your CYA of 57. What am I missing?
 

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