Difficulty bringing pH down, and odd TA Results - blue to yellow but no chlorine

[QPSUtah]

Just refilled an in-ground spa for a customer. Upon filling, the TA was very high. I tested 180 TA initially with a pH above 8 and requiring upwards of 50 drops of acid demand to bring it down. I left my test kit with the client who was regularly adding acid to bring it down (thought I don't know how much was added total).

I went back today and am still getting high pH, requiring about 20+ drops of acid demand. When I tested TA, it was light blue (see pic) and would immediately turn to light green. I mistakenly thought this was my TA test so added some baking soda/"Alkalinity" product. But doing some addl research, I see that in the present of a lot of chlorine, the TA may start light blue and turn yellow. However, the chlorine is basically zero. I get some initial pink when I add the powder, but then it goes clear without adding any titrating agent.

I brought a sample home and will take it to Leslie's tomorrow for their analysis. But in the meantime, I'm getting the followig...

Chlorine 0
TA 110 (light blue to yellow)
pH > 8 (40+ drops acid demand to bring within range)
CH 400

I didn't test CYA as it's a fresh fill and only liquid chlorine has been added.

My reagents don't seem bad. But maybe some of them are starting to turn. They are all less than one year old, purchased in May of this year.

In the pic, you can also see a "scum" ring around the tub. Not sure what might have caused that.

 

[PoolStored]

If you carry reagents around in a hot truck all summer, they will degrade. Might be best to replace reagents more often.
Yes, yellow TA is typically high FC. It is still valid.
Not sure why the FC would be 0 on the test. Is the 0870 still white? or are you using OTO?
Are you sure it is scum and not calcium scale? Your CSI is .64...which would likely cause scale (assuming your results and 80 degree water. Higher temp would be higher scale.
Your fill water has high TA and CH. With a new fill, you will want to be diligent with acid additions (daily or more often) until TA comes down to 50. This will avoid scale. While you are in the lowering process, lower the pH to 7.2, allow it to rise to 8, then repeat until TA is 50-70, then STOP lowering it to 7.2...and only lower to 7.8. Doing this will lower the TA fairly rapidly (couple times a day test and treat) and help you avoid scale.

 

[QPSUtah]

If you carry reagents around in a hot truck all summer, they will degrade. Might be best to replace reagents more often.
Yes, yellow TA is typically high FC. It is still valid.
Not sure why the FC would be 0 on the test. Is the 0870 still white? or are you using OTO?
Are you sure it is scum and not calcium scale? Your CSI is .64...which would likely cause scale (assuming your results and 80 degree water. Higher temp would be higher scale.
Your fill water has high TA and CH. With a new fill, you will want to be diligent with acid additions (daily or more often) until TA comes down to 50. This will avoid scale. While you are in the lowering process, lower the pH to 7.2, allow it to rise to 8, then repeat until TA is 50-70, then STOP lowering it to 7.2...and only lower to 7.8. Doing this will lower the TA fairly rapidly (couple times a day test and treat) and help you avoid scale.

This test kit mostly sits in the office, so I still doubt the reagents are bad. Yes, using 0870. No discoloring there. I've intermittently tested other water, and get the normal "green" TA color in other spots. But yeah, very weird I'm getting the blue TA color with no chlorine present. He has a chlorine generator that has not been generating chlorine because there has not been enough salt in there.

 

[PoolStored]

Clean the vial with rubbing alcohol and dry. See if that fixes it...

 

[QPSUtah]

Clean the vial with rubbing alcohol and dry. See if that fixes it...

I brought a sample home and tested ina clean jar here. Using the DPD method, I read 0 ppm chlorine (I get a pink color that disappears as soon as I invert). Using FAS-DPD, I get a pink color after adding 0870 but then no amount of 0871 can make it go clear. So maybe one of those two reagents are bad.

But still, my guess is there would be very little chlorine in the spa right now as the salt cell has not been generating anything due to low salt.

 

[JamesW]

Seems like the reagent is bleaching out.

Dilute the sample with distilled water and retest.

Pool Water...........Distilled......Multiply Result by
1...................................1........................2

1...................................2........................3

1...................................3........................4

1...................................4........................5

1...................................9........................10

Use FASDPD and use an OTO test to compare results.

 

[QPSUtah]

Seems like the reagent is bleaching out.

Dilute the sample with distilled water and retest.

Pool Water...........Distilled......Multiply Result by
1...................................1........................2

1...................................2........................3

1...................................3........................4

1...................................4........................5

1...................................9........................10

Use FASDPD and use an OTO test to compare results.

Good idea. As a follow up, I think he was mistakenly adding chlorine instead of acid, which is why the pH has remained unchanged and I was getting the blue TA result. I brought it back to the office and tested with fresh reagents and tested a 10 ml sample and just added 0871 til it went clear. It tested at 60 ppm chlorine. So I’ll have him leave the cover off and add some thiotrine to bring it down.

 

[JamesW]

As a follow up, I think he was mistakenly adding chlorine instead of acid, which is why the pH has remained unchanged and I was getting the blue TA result.

The pH test is not accurate with FC over 10 ppm.

You can use 3% hydrogen peroxide to lower the FC.

2 oz of 3% hydrogen peroxide will lower the FC by 1 ppm for 1,000 gallons.

There is virtually no effect on the chemistry.

The pH might drop a tiny bit, but that is all.

2H₂O₂ + OCl^-+ HOCl --> 2O₂ + 2H₂O + H⁺ + 2Cl^-

 

[QPSUtah]

The pH test is not accurate with FC over 10 ppm.

You can use 3% hydrogen peroxide to lower the FC.

2 oz of 3% hydrogen peroxide will lower the FC by 1 ppm for 1,000 gallons.

Thank you so much.

 

[QPSUtah]

The pH test is not accurate with FC over 10 ppm.

You can use 3% hydrogen peroxide to lower the FC.

2 oz of 3% hydrogen peroxide will lower the FC by 1 ppm for 1,000 gallons.

There is virtually no effect on the chemistry.

The pH might drop a tiny bit, but that is all.

2H₂O₂ + OCl^-+ HOCl --> 2O₂ + 2H₂O + H⁺ + 2Cl^-

How quickly does H2O2 neutralize chlorine?

 

[JamesW]

How quickly does H2O2 neutralize chlorine?

Seconds to minutes depending on circulation.

Note that it might not work on bromine.

 

[QPSUtah]

Seconds to minutes depending on circulation.

Note that it might not work on bromine.

I think I’ve figured it out. He has a pool spa combo and whoever shut the pool down didn’t adjust the programming, so in pool mode it was still circulating the spa and running the swcg at 100%. So chlorine was through the roof. Yesterday there was still a low salt light on but maybe it was still generating some chlorine. I’ve added some h202. Seems to be now down to 30 ppm chlorine, testing at 3:1 distilled to spa water (7.5 ppm on 10ml diluted sample). Was probably over 100 ppm. I’ll need more h202. Then I’ll address pH.

For reference, took sample to Leslie’s and they weren’t even close. Tested my chlorine at 10 ppm. Off by a factor of 10 at least. Granted, maybe their testing equipment doesn’t even test that high. They also tried to tell me my alkalinity was 0 but my ph was over 8.

 

[JamesW]

For Spas, it might be best to drain and refill if it can be done safely.

A Spa can float like a pool if the ground water is high.

For 750 gallons or less, a drain and refill can sometimes be the fastest and easiest solution.

 

[QPSUtah]

We just drained and filled it for him. Previous maintenance group had let the water really go to pot. So yeah, it probably is, but reluctant to tell him we need to start over again... It's a larger spa, 1500 gallons or so. I don't mind investing the time into it. Builds the relationship, and it's an investment in my own education as I encounter these types of scenarios I can also train my techs on if needed.

 

[PoolStored]

Test the refill water for TA and CH.

 

[QPSUtah]

So here is what I think happened.

Visit 1 - we refilled the in-ground spa. TA was very high, 180-200, and acid demand reagent was requiring 50+ drops to bring pH into range. I added a few pounds of pH minus but pH wasn't dropping much, but I instruct client on testing pH and adding acid and left. I also added salt to the spa for the chlorine generator.

Visit 2 - I show up a few days later and that is when I get the results and picture that started this thread. The "low salt" light was on the salt cell and I assumed the cell wouldn't generate chlorine with low salt indicated, but perhaps it was, or perhaps the client was mistakenly adding chlorine rather than acid. This led to my confusion when doing chlorine tests. I was assuming the chlorine level should be 0, but after diluting the sample with distilled water later at the office, I could get consistent chlorine readings. But apparently, the DPD method goes clear upon inversion at high chlorine levels, and I was adding so much 0871 in the FASDPD test the sample would turn wine colored, I was just sure something was off in my testing or reagents. But after diluting, was able to get the FAS DPD test and DPD test to agree with one another. I also added some additional salt to bring it up to the correct level at this visit.

Visit 3 - The next day I show up with a bunch of H202. Of course, by this point, no one has been swimming in the spa, naturally, and the salt cell is generating chlorine as the salt level is sufficient and it's well over 150 ppm. The other thing that happened is whoever shut the pool down did not adjust his schedules and valves correctly. So on both "spa" mode and "pool" mode, the valves are circulating the spa water. So he has 100% chlorine generating output with his IC40 for a 1500 gallon spa and it's running probably 16+ hours a day. So yeah, the chlorine was then super high the next day. I add enough H2O2 and am able to bring it down to about 30 ppm, but I don't have enough H2O2 to bring it down further. I do adjust his schedules and salt cell output to a reasonable level.

Visit 4 - The day after that, i show up with additional H2O2, bring the chlorine down to about 4 ppm, then test alkalinity and pH. I'm now getting good results for both and leave with TA testing 110 or so and pH testing 7.6.

So thanks for the input and help on this matter. I think I was able to resolve it and learned a ton in the process.