new K-1000/K-1001 both reading very high vs TF-100 FAS/DPD

[Gx]

This is my 6th season with this pool. Previously, the K-1000 & K-1001 very closely matched the results from the TF-100 DPD powder test (& AquaCheck strips).
My pool has been quite stable for years, so I traditionally only do the DPD powder test weekly.

This year, both the K-1000 & K-1001 are reading off the chart (10ppm) high, while TF-100 DPD powder test shows 3 ppm.
My nose/tongue/eyes test would say that the DPD powder result is closer, as do the AquaCheck test strips.
All of these chemicals were purchased this year. Expiration on K-1000, K-1001 is 2019, 2020.
pH is 7.7, TA 70, cya 80, cc <= 0.5

How can my new K-1000 & K-1001 kits results be so wrong?

 

[Jimrahbe]

gx,

I am not much of a chemical expert, but I suspect that you have put something in the water that is interfering with the color match tests...

What chemicals have you recently added???

Let's see what our other members have to say..

Thanks for posting,

Jim R.

 

[Gx]

My chemical usage this year is the same as in past years: Arm&Hammer baking soda, muriatic acid from Lowe's (green jug), PuriTech granulated CYA.
Thanks to TroubleFreePool, I don't use much. I also use 20MuleTeam borax (40).

Two issues opening this year: pH was low, which never happens. I ended-up shocking twice, after raising pH with borax.
I tried a ChlorinatorPro salt cell, which I had to return. During this ~2 weeks, I used 3" trichlor tablets.

 

[Gx]

OK, I have now realized one anomaly, which I neglected to mention:
As my salt cell evidently died this spring, it was giving bad salt level readings.
So, I put in too much salt. My level is elevated, ~3700.
Would this cause the K-1000 & K-1001 to read high?

 

[duraleigh]

Not related to salt.

Typically, we think of the OTO (K-1000) test as very dependable but not accurate.....accuracy is the domain of the FAS/DPD (powder) test. I am not sure why you say the K-1000 is giving you a 10 ppm result.....it really only goes to 5 ppm.

Nonetheless, I would suggest you use the kits as described above.....K-1000 for the presence (but not accurate) of chlorine and when you REALLY want to know the exact amount of chlorine, use the FAS/DPD.

I also suggest you are doing FAR too many chlorine tests. Retire the K-1001....it adds no information that the suggested two tests can not provide and then give the strips to somebody you don't like.

 

[Gx]

My K-1000 shows "5 10" at the highest level, & my reading is above (darker than) that !

I don't want the trouble/expense of doing the powder test every time, & haven't had to for 5 years !

So, the K-100x should have only two gradations, "yes" & "no" ?!? Why do they have 5 ?

I got the K-1001 this year only because of these odd readings.

For 5 years, the results have matched. Now, they are nowhere close! Surely there is _some_ chemical explanation.

@chemgeek, where u at ?

 

[Lilypad]

The K-1000 tests from .5-5ppm Chlorine. The “10” that you mention is for Br which is bromine. As Duraleigh mentioned, the FAS-DPD is exact and measures a higher number.