Why would my FC go higher than anticipated

[Kelly Gordon]

I'm just opening my Minnesota pool for the 2024 year. Tested the water yesterday when we first turned the pump on, and the FC was zero, as anticipated. Pool Math recommended I add 1.7 jugs of 12.5% chlorine to raise the FC to 4, so I did that a few hours ago. Just went out to measure and the FC is measuring above 20.

I'm not worried; the water is cloudy after adding the chlorine, but I know that's part of my process. But I am curious why the levels are so much higher than Pool Math said to expect. (The SWG cell is off still, by the way. Waiting for the heater to get my water up to a warmer level.) Any chemists want to take a stab?

 

[PoolStored]

1. Testing Error. Use 10mL sample to test. Each drop is .5.
2. You used a 25ml sample instead of a 10ml sample...which made the amount of FC 2.5x actual.
3. Dirty equipment, clean your tube with alcohol or bleach and retest.

Clean and retest...carefully.

 

[bobloblaw42]

Did the pool run 24-48 hours after initial pump start? If not, your first sample may not have been representative of the average of the pool and instead representative of wherever you pulled your sample.

 

[Kelly Gordon]

So you were half right. I did a 10ml sample and forgot that each drop is .5.

But I did it again, with a clean tube, being very careful to count each drop, and I stopped adding solution after 32 drops. The sample was still very pink, although not as hot pink as it was originally.

Could my R871 solution be bad?

 

[Kelly Gordon]

Did the pool run 24-48 hours after initial pump start? If not, your first sample may not have been representative of the average of the pool and instead representative of wherever you pulled your sample.

The pool pump had run for 24 hours before I added bleach. I then waited two hours to test. So I don't think it's an individualized issue.

 

[mgtfp]

What is your definition of a jug? I suspect that's where we have a mismatch between what you were adding and what PoolMath thought you'd be adding.

 

[bobloblaw42]

The pool pump had run for 24 hours before I added bleach. I then waited two hours to test. So I don't think it's an individualized issue.

I was referring to your sample @ zero FC. Did that have 24 - 48 hours pump run time before sample was taken? If not, it is possible that you did in fact still have FC upon opening, just not where you pulled that initial sample from due to insufficient time to equalize water chemistry after sitting uncirculated during winter. If yes, then we've at least eliminated one possible cause for your original question.

 

[proavia]

How old are your K-2006 reagents?
Are any with listed expiry dates past that date?

 

[Kelly Gordon]

What is your definition of a jug? I suspect that's where we have a mismatch between what you were adding and what PoolMath thought you'd be adding.

I added 2 gallons of 12.5% liquid chlorine. According to the Pool Math app, that should raise my FC by 6.2 ppm.

I am measuring more than double that.

 

[Kelly Gordon]

I was referring to your sample @ zero FC. Did that have 24 - 48 hours pump run time before sample was taken? If not, it is possible that you did in fact still have FC upon opening, just not where you pulled that initial sample from due to insufficient time to equalize water chemistry after sitting uncirculated during winter. If yes, then we've at least eliminated one possible cause for your original question.

Yes. I got zero FC after the pump has been running close to 24 hours. And that’s pretty normal for me. The pool was been closed since early October ‘23. I try to have the water balanced when we close - around 3 ppm FC - but it’s all gone by the time spring comes. (As is all the CYA, but that’s another post.)

 

[PoolStored]

Could my R871 solution be bad?

Yes...

 

[Chasarms]

The most likely explanation is that the reagent is expiring or expired.

This may actually be a time where free tests at the pool supply are worth something. I wouldn't trust them for calculating what to add, but if you stop by and have them test the water and it is in the ball park of what Pool Math says, it points to the reagent. If their number is also really high, then you got a super hot batch of shock!!!!! (not likely at all)

There's not a whole lot else that it could be.