All levels are correct, but pool won't hold chlorine

[danielpatrick]

I've been stuck for the past couple of days trying to figure this out.

I use a proper test kit to test levels and all other levels check out. I also use my local pool shop to test when my CYA drops below 30 since this can't be tested in the liquid Taylor kit that I use (if I assume 0, then I end up overdosing). My kids displace a lot of water when playing (they create "waves" that splash over) so I have to sometimes get tested after that (it's only reason I can figure why CYA would fall).

Since pool start up over 2 years ago, it's largely been incident free. I sometimes have a lot of demand, but usually in the summer. When I haven't been able to get chlorine to stick, it's always been dirty filters or a algae bloom that's in process of getting knocked out.

Latest measurements (from a Leslie's disc test because chlorine doesn't show up on the Taylor liquid drip test):

Free CL 0.32
Total CL 0.59
pH 7.4 * (precisely matches my test precisely)
Total Alk 107
Calcium 266
CYA 41 * (approximately matches my test, since the Taylor test is more of a range when outside of a specific value)
Iron 0.1
Copper 0.1
Phosphates 3704
TDS 2700

About 5 days ago I added calcium because my levels were low (<200). That spiked my pH to 7.8, which I dropped back down to 7.4 a couple of days later. Since the addition of calcium I've not been able to get chlorine to stick. I've used multiple gallons of 12.5% liquid chlorine over the past 3 days and it's like nothing was added (test wise). I've dosed to get to even 6 FC and it never even gets there.

I only use liquid chlorine, I don't use pucks, and I don't use shock.

As you might imagine, Leslie's is suggesting I do a partial drain to solve for the high Phosphates and TDS. I've always had high phosphates (it cycles, but out the tap it's always 200 or higher). TDS is usually high as well, somewhere between 1000-2700 based on my logs. I usually ignore both and I haven't had to drain before.

I have noticed for this pool season I've had to add chlorine on a more regular basis than previous years. It could be just a warmer season or the slightly smaller (but properly sized) filter system I installed earlier this year which seems to require more cleaning than before. The pool typically gets to 80º on its own, and when the heat pump is turned on, it can get up to 85º or higher. Since adding the calcium, I haven't been using the heater.

I had a big argument with the wife (the former steward of the pool) about draining because she says it's nonsense. But I don't know where else to begin! I'm a follower of the Pool School and I even looked at other threads to see if there are any clues. But in most cases those individuals had high CYA.

Are there any suggestions to solve this? Is this the one time that calls for a partial drain? We're loathe to do so, but I will if that's what it takes.

 

[PoolGate]

What is your CYA right now with your test? There is a CYA eating bacteria that leaves ammonia as a byproduct. That ammonia will neutralize all of your chlorine in 15 minutes after adding it until the ammonia is gone which can take a lot of chlorine. You can test for ammonia with an aquarium test kit.

 

[newdude]

There's a free ammonia test. Add FC to 10 and check it 30 mins later. If most if it is gone, then it's ammonia. The cure is to test/dose back to 10 every 30 mins until it holds.

However, with the CYA level in doubt, and yes, Leslie's results are big fat doubts, do the ammonia test in the evening once the sun is real low in the sky and not consuming much.

If you lose a bunch of FC in 30 mins with little to no UV, it'll be ammonia.

If the FC mostly holds, Overnight Chlorine Loss Test tonight. If you lose FC overnight with no UV, then it's algae and you need to SLAM Process.

If you pass the ammonia test and the OCLT, then the CYA level is low and the sun is just naturally burning off large amounts of FC with no protection.

*assuming the chlorine is fresh with a recent manufacturing date, from a trusted source.

 

[Rocket J Squirrel]

@danielpatrick you need to augment your K-2005 test kit with the K-1515 so you can measure free chlorine more accurately and at higher levels.

 

[danielpatrick]

What is your CYA right now with your test? There is a CYA eating bacteria that leaves ammonia as a byproduct. That ammonia will neutralize all of your chlorine in 15 minutes after adding it until the ammonia is gone which can take a lot of chlorine. You can test for ammonia with an aquarium test kit.

The CYA tests at 40 with my Taylor set. I also keep a couple of aquariums, and using the ammonia test, the result is 0.

 

[danielpatrick]

There's a free ammonia test. Add FC to 10 and check it 30 mins later. If most if it is gone, then it's ammonia. The cure is to test/dose back to 10 every 30 mins until it holds.

However, with the CYA level in doubt, and yes, Leslie's results are big fat doubts, do the ammonia test in the evening once the sun is real low in the sky and not consuming much.

If you lose a bunch of FC in 30 mins with little to no UV, it'll be ammonia.

If the FC mostly holds, Overnight Chlorine Loss Test tonight. If you lose FC overnight with no UV, then it's algae and you need to SLAM Process.

If you pass the ammonia test and the OCLT, then the CYA level is low and the sun is just naturally burning off large amounts of FC with no protection.

*assuming the chlorine is fresh with a recent manufacturing date, from a trusted source.

Sure, I'd agree that Leslie's test is to be looked at in doubt. But! 40 CYA is also what I'm seeing in my Taylor drip test as well. I just retested based on Newdude's request, and it's still 40.

The chlorine is the yellow trade buckets (12.5% strength), maybe 2 weeks old at most. Stored in the shade, away from sun.
I did a liquid test for ammonia using a liquid test kit I use for my aquariums. It registers at 0.

 

[danielpatrick]

@danielpatrick you need to augment your K-2005 test kit with the K-1515 so you can measure free chlorine more accurately and at higher levels.

Thank you for the suggestion. I'm surprised for a need to test at a level higher than 10? I usually keep this pool at 3, testing and balancing on a daily basis.

 

[Rocket J Squirrel]

We have a page all about test kits. Have a look: Test Kits Compared

 

[Bperry]

Thank you for the suggestion. I'm surprised for a need to test at a level higher than 10? I usually keep this pool at 3, testing and balancing on a daily basis.

That’s likely your issue. 3ppm is the absolute bare minimum when using a SWCG if your CYA is 40 and there’s no algae. It should really be raised up to around 7ppm each day.

You likely have an algae bloom starting OR you have ammonia. There’s no need to drain the water but the answer to both is more chlorine. But you’ll need the more accurate FC test to SLAM. If you haven’t been using a FAS-DPD test for that it’s likely related to the inability to hold chlorine as well.

 

[PoolStored]

I'm surprised for a need to test at a level higher than 10?

You need to be able to test at accurate levels to determine if you have algae...Link-->Overnight Chlorine Loss Test

If you fail OCLT, then you need to slam and with CYA of 40, you need to be able to test up to SLAM level (16FC with CYA 40) when you follow this process to rid algae...Link-->SLAM Process

I usually keep this pool at 3, testing and balancing on a daily basis.

This is likely the cause of your chlorine/algae problem...you should follow this link...-->FC/CYA Levels

 

[newdude]

I'm surprised for a need to test at a level higher than 10?

Many of us with SWGs need 10 with a 70+ CYA.

LC folks need it for SLAMs, but they also need the reliability of 0 to 10 with the fas/dpd kit.

The block test isn't accurate per Taylor's own say so. It only tests TC when it does, and 4+0= 4 and 1+3=4 tell two entirely different stories. So even if it was accurate, it doesn't tell you what you need to know.

I usually keep this pool at 3, testing and balancing on a daily basis

I'm surprised you haven't had issues sooner. Your profile days SWG but you're using liquid chlorine, which one is it ? Either way, a 3 is way too low.





You should be targeting the high side of 'in range' if not over, to fall back into range with any swing. This allows wiggle room for any unforseen events like a particularly high UV loss day, or a big storm.

Sure, I'd agree that Leslie's test is to be looked at in doubt. But! 40 CYA is also what I'm seeing in my Taylor drip test as well. I just retested based on Newdude's request, and it's still 40.

The chlorine is the yellow trade buckets (12.5% strength), maybe 2 weeks old at most. Stored in the shade, away from sun.
I did a liquid test for ammonia using a liquid test kit I use for my aquariums. It registers at 0.

Ok GREAT. 40 it is, which should hold chlorine just fine once it's added.

With ammonia and weak supply all but ruled out, were back to algae. It's time to Overnight Chlorine Loss Test

 

[danielpatrick]

That’s likely your issue. 3ppm is the absolute bare minimum when using a SWCG if your CYA is 40 and there’s no algae. It should really be raised up to around 7ppm each day.

You likely have an algae bloom starting OR you have ammonia. There’s no need to drain the water but the answer to both is more chlorine. But you’ll need the more accurate FC test to SLAM. If you haven’t been using a FAS-DPD test for that it’s likely related to the inability to hold chlorine as well.

Thanks for pointing out for SWGG. I realized my profile said that from back when this pool was starting up (doh!) but we abandoned that. It's been a chlorine pool since start up.

 

[danielpatrick]

Many of us with SWGs need 10 with a 70+ CYA.

LC folks need it for SLAMs, but they also need the reliability of 0 to 10 with the fas/dpd kit.

The block test isn't accurate per Taylor's own say so. It only tests TC when it does, and 4+0= 4 and 1+3=4 tell two entirely different stories. So even if it was accurate, it doesn't tell you what you need to know.

I'm surprised you haven't had issues sooner. Your profile days SWG but you're using liquid chlorine, which one is it ? Either way, a 3 is way too low.


View attachment 531382
View attachment 531381

You should be targeting the high side of 'in range' if not over, to fall back into range with any swing. This allows wiggle room for any unforseen events like a particularly high UV loss day, or a big storm.


Ok GREAT. 40 it is, which should hold chlorine just fine once it's added.

With ammonia and weak supply all but ruled out, were back to algae. It's time to Overnight Chlorine Loss Test

Yeah, really sorry about SWGG on the profile, didn't catch that until too late.

It's a liquid chlorine pool. I usually target approx. 45 CYA and 3 PPM Cl, which has been manageable for 2 years since I manage the chemistry on a daily basis. The other reason I target 3 PPM is the guidance for my heat pump since it indicates higher levels would be corrosive to the heat exchanger:

 

[reggiehammond]

It's been a chlorine pool since start up.

Just FYI - a SWCG pool and a liquid/powder chlorine pool are the same thing.
A SWCG just uses electrolysis and salt to make free chlorine, which I would argue is an immensely better way.

 

[reggiehammond]

Yeah, really sorry about SWGG on the profile, didn't catch that until too late.

It's a liquid chlorine pool. I usually target approx. 45 CYA and 3 PPM Cl, which has been manageable for 2 years since I manage the chemistry on a daily basis. The other reason I target 3 PPM is the guidance for my heat pump since it indicates higher levels would be corrosive to the heat exchanger:

View attachment 531408

As you'll learn here at TFP - the industry guidance for low FC is based on ignorance toward the effect of CYA. If you run at 3ppm, even if you test and dose daily, you will certainly end up with algae. Your CYA just has too much of the effectiveness of the FC restricted. Trying to maintain levels based on the heat exchanger chart is a fools' errand.

You can skip right into SLAM Process, in my opinion.

 

[danielpatrick]

Many of us with SWGs need 10 with a 70+ CYA.

LC folks need it for SLAMs, but they also need the reliability of 0 to 10 with the fas/dpd kit.

The block test isn't accurate per Taylor's own say so. It only tests TC when it does, and 4+0= 4 and 1+3=4 tell two entirely different stories. So even if it was accurate, it doesn't tell you what you need to know.

I'm surprised you haven't had issues sooner. Your profile days SWG but you're using liquid chlorine, which one is it ? Either way, a 3 is way too low.


View attachment 531382
View attachment 531381

You should be targeting the high side of 'in range' if not over, to fall back into range with any swing. This allows wiggle room for any unforseen events like a particularly high UV loss day, or a big storm.


Ok GREAT. 40 it is, which should hold chlorine just fine once it's added.

With ammonia and weak supply all but ruled out, were back to algae. It's time to Overnight Chlorine Loss Test

The OCLT guidance says to get the levels to at least 3PPM. I can't even get it to register that, even if I test a couple of hours later.
Do I modify this as follows:
1. Dose pool to 10PPM (0 FC -> 10 FC) (128oz of 12.5% liquid Cl for a 17.5K pool, according to PoolMath) in evening
2. Run pump overnight
3. Test again in the morning?

 

[newdude]

Yeah, really sorry about SWGG on the profile, didn't catch that until too late

Noooooooooo problemo. It's all cleared up now.

I usually target approx. 45 CYA and 3 PPM Cl, which has been manageable for 2 years since I manage the chemistry on a daily basis.

Can you explain further ? If we all lose about 4 ppm mid season, a once daily dose would need be 7 in order to land at 3. Or, playing with fire at 3 swinging to 0.

7 to 3 while still too low in the end would have a better chance of working for a spell.

The other reason I target 3 PPM is the guidance for my heat pump since it indicates higher levels would be corrosive to the heat exchanger:

The industry doesn't recognize the FC/CYA relationship. As such, tap water with 0 CYA and 1 ppm FC has a higher HOCL level than your 40 CYA and 16 FC. ( And tap water may have up to FOUR ppm FC. Disregard industry advice that doesn't listen to science.

 

[danielpatrick]

Noooooooooo problemo. It's all cleared up now.

Can you explain further ? If we all lose about 4 ppm mid season, a once daily dose would need be 7 in order to land at 3. Or, playing with fire at 3 swinging to 0.

7 to 3 while still too low in the end would have a better chance of working for a spell.



The industry doesn't recognize the FC/CYA relationship. As such, tap water with 0 CYA and 1 ppm FC has a higher HOCL level than your 40 CYA and 16 FC. ( And tap water may have up to FOUR ppm FC. Disregard industry advice that doesn't listen to science.

It seems I've been content playing with fire, as my day normally starts out with 1ppm. I will try my hand at 7ppm once I get a handle on this situation. I will start with SLAM level + OCLT and share the results in this thread.

1. SLAM to 10ppm target
2. Retest this evening, bring back to 10ppm if levels aren't there (with pump running overnight)
3. OCLT with test in the AM.

Pool has a solar cover but I'm sure it doesn't create a total absence of light...

Only thing I'm not clear on is the frequency I can aim for 10ppm while in SLAM process. I'm WFH, so I could dose it every hour if I wanted to.

 

[PoolStored]

It seems I've been content playing with fire, as my day normally starts out with 1ppm.

1. SLAM to 10ppm target

Slam level for CYA is 16 FC.

Only thing I'm not clear on is the frequency I can aim for 10ppm while in SLAM process. I'm WFH, so I could dose it every hour if I wanted to.

Print this out. Read it three times. Keep in with you. I found having hard copy really helps for reference. Link-->SLAM Process

Every hour is a "bit extreme," but in the beginning, really helpful. Every two hours is fine after your initial large losses...but then again I'm extra and slammed every 1-2 hours from 7am to 1-2am for 8 days (would have been about 4 days but I didn't know stuff can grow in ladder tubes)..but I was facing a July 4th holiday weekend. Happy to report a few years of no slams and my FC never sniffs minimums.

 

[proavia]

1. SLAM to 10ppm target

You are not raising FC to 10 and doing a SLAM Process.
SLAM level for your CYA of 40 is FC of 16 - as indicated in the charts in post #11.
You are merely raising your FC to 10 to start your Overnight Chlorine Loss Test.
Unfortunately, you will be unable to accurately test the starting and ending FC of the OCLT without the Taylor K-1515 testkit (R-0870 and R-0871 reagents).

Don't confuse the word "shock" with SLAM - they are not interchangeable. SLAM Process