How often do you get a "bum" reading with your test kit?

[71ailmar]

It's happened 2-3 times already over the course of 6+ months maybe (with FC/CC, not with any of the other chemistry readings) and it's usually a weirdly low reading compared to what I should have so I do another test immediately to double check and find the 2nd test to show a higher, more accurate reading of where I'm supposed to be.

Yesterday:
FC 11.5 and < 0.5cc
pH 7.8 (added 1/4 gal of MA to drop it just a little)
TA 50
CYA 55 (I'll be adding stabilizer once it delivers in a couple of days)

Those readings were just before we had a few friends over yesterday (total bather load of 8 people) and the SWG ran the whole time plus our usual run time overnight so testing the water today I would assume to be a similar level or couple points lower.
Just now when I tested FC it showed 6 with a CC of 2. I knew immediately that couldn't be correct unless my new SWG was on the fritz so I
re-tested and got FC 9.5 w CC of < 0.5 which is what I would have expected.
How often do false readings come through on FC testing?

 

[wireform]

You may have contamination in the chlorine vial. Clean the vial and bean with alcohol then with some dish soap and rinse well with hot water.

 

[Bperry]

It's happened 2-3 times already over the course of 6+ months maybe (with FC/CC, not with any of the other chemistry readings) and it's usually a weirdly low reading compared to what I should have so I do another test immediately to double check and find the 2nd test to show a higher, more accurate reading of where I'm supposed to be.

Yesterday:
FC 11.5 and < 0.5cc
pH 7.8 (added 1/4 gal of MA to drop it just a little)
TA 50
CYA 55 (I'll be adding stabilizer once it delivers in a couple of days)

Those readings were just before we had a few friends over yesterday (total bather load of 8 people) and the SWG ran the whole time plus our usual run time overnight so testing the water today I would assume to be a similar level or couple points lower.
Just now when I tested FC it showed 6 with a CC of 2. I knew immediately that couldn't be correct unless my new SWG was on the fritz so I
re-tested and got FC 9.5 w CC of < 0.5 which is what I would have expected.
How often do false readings come through on FC testing?

Side note that your pH test isn’t valid when the FC is over 10. That’s one way to get a bum result.

 

[Saturn94]

I almost never get a bum reading (I keep test equipment squeaky clean and replace reagents when expired). Let’s hope I didn’t just jinx myself, lol.

 

[magiteck]

I’ve only had this happen when not adding enough of the DPD powder. It should be 1 heaping spoonful or 2 level spoonfuls. Sometimes now if I don’t feel like my heaping spoonful was enough, I’ll add a bit more.

A little too much won’t affect anything but too little can.

 

[71ailmar]

Side note that your pH test isn’t valid when the FC is over 10. That’s one way to get a bum result.

Why do I feel like I knew this but didnt remember?! LOL
Thank you for that reminder. So how far off would pH be when FC is a bit over 10, usually?

Because our SWG was on the fritz recently and we had been out of town, I had added large amounts of LC while waiting to get the SWG replaced. Now that it's replaced, the SWG is running at what it usually needs to run at but I still have effects from LC in the pool which is why my FC is over 10 right now. Over the next few days I think it'll drift back down to normal levels. Because my SWG is undersized, I might even have to supplement with a little chlorine every now and then if I want to keep my levels around 5. Otherwise I have to run the pump much longer.

 

[superdave5599]

Why do I feel like I knew this but didnt remember?! LOL
Thank you for that reminder. So how far off would pH be when FC is a bit over 10, usually?

Because our SWG was on the fritz recently and we had been out of town, I had added large amounts of LC while waiting to get the SWG replaced. Now that it's replaced, the SWG is running at what it usually needs to run at but I still have effects from LC in the pool which is why my FC is over 10 right now. Over the next few days I think it'll drift back down to normal levels. Because my SWG is undersized, I might even have to supplement with a little chlorine every now and then if I want to keep my levels around 5. Otherwise I have to run the pump much longer.

I think the reason the PH test isn't valid with FC over 10 is because the chlorine will bleach out some of the red and skew the reading you'd get from looking at the red scales. I doubt there is/could be a standard adjustment.
I haven't seen any comment about using the chlorine neutralizer in that vial, though. I wonder if that would affect the PH reading? Or, could I take a sample of pool water out and let it sit in the sun to consume enough chlorine to reduce to below 10, and check the PH later in the day? Would sitting there in a measuring cup all day do anything to the PH? Or you could get a meter.

 

[wireform]

There is a way to dilute the chlorinated water to get a stable PH reading but can't remember now what that is.

 

[Bperry]

Why do I feel like I knew this but didnt remember?! LOL
Thank you for that reminder. So how far off would pH be when FC is a bit over 10, usually?

Because our SWG was on the fritz recently and we had been out of town, I had added large amounts of LC while waiting to get the SWG replaced. Now that it's replaced, the SWG is running at what it usually needs to run at but I still have effects from LC in the pool which is why my FC is over 10 right now. Over the next few days I think it'll drift back down to normal levels. Because my SWG is undersized, I might even have to supplement with a little chlorine every now and then if I want to keep my levels around 5. Otherwise I have to run the pump much longer.

I think someone mentioned pH tends to read high when the FC is over 10. But don’t hold me to that.

 

[Saturn94]

PH - Further Reading

www.troublefreepool.com

 

[kellyfair]

I can honestly say I have never had a bum reading. Now, have I lost count of drops? Yep, I have gotten distracted many a time.

 

[Newdude]

It's crazy. Eventhough I know DARN well I have more than 5 FC, there's always this *phew* moment at 10 drops and I usually miss 11 then have to add it back mentally after 12 and then I'm no longer sure anymore if I did in fact miss it.

But when I end up with 20something, I *phew* again because it's a moot point.

 

[kellyfair]

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