K-1001 vs FAS-DPD

EndlessPhill

New member
Dec 8, 2019
2
DFW TX
Hi everyone.

I got my endless pool w/ a separate spa several months ago, and have been using the TF-100 since day one with great success. This site and guide has been tremendous in my success and ease, so thank you all in advance!

After a few weeks of having my new pool/spa, I switched from using the included K-1000 to a K-1001 for daily testing, mostly because my spa burns chlorine at 101 degrees and I wanted a more accurate daily test. I still do the full FAS-DPD weekly. I haven't had a problem at all!

Yesterday after using the pool, I used the K-1001 and saw I was around 3 FC on the pool side, and 2 on the spa side. Using my fresh 10.5% liquid chlorine, I added the proper amounts to get me back up to around 6-7 FC (my CYA is about 35 on both sides) it was approx 7oz for the pool and 1.5oz for the spa (2000 gals and 333ish gals respectively). This is fairly normal, except the pool only needs chlorine about once a week, the spa daily / every other day.

So here's my confusion. Today, I did my biweekly filter cleaning, and afterwards did the full FAS-DPD test. I got very high FC results which surprised me. The pool came out at 11 FC, and the spa at 16 FC! This is about 16 hours after I added the chlorine yesterday with no use since. I reused the K1001 just to be sure, and things got even weirder. The pool showed darker than 5 FC on the block (expected if the FC really is 11) but the spa only showed 3 (when it really should be 16!)

I definitely trust the FAS-DPD, but why would the k-1001 not line up at all? This is the first time I've seen that in a little over a month I have been doing this.

I thought I knew what I was doing, but now I am not sure. Any ideas?
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
I believe you are seeing first-hand the differences between the 1000 & 1001. Take a look at these threads:
 

EndlessPhill

New member
Dec 8, 2019
2
DFW TX
Yes, I am aware of the difference between the 1000 and the 1001, my understanding is the 1001 should be close to the FAS-DPD.

However those threads do point out a difference. Could the discrepancy on my spa side be because the FC is very high, so the FAS-DPD is correct but that's why the plain DPD reads low?

Regardless, I'm coming to the conclusion that using it as a daily test should still only be used to show me that I still have chlorine, instead of how much. Much like the K1000 was recommended for in the TF-100 kit.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
16,209
Tucson, AZ
The reagents in the K-1001 (R-0001 and R-0002) are only designed to read FC levels below 10ppm. When the FC levels are higher than that, you can get bleaching of the reagent and get a false low reading. In fact, if the FC were high enough, your K-1001 could go completely clear and make you think there was NO FC in the water. Try adding adding 10 drops of the R-0001 and R-0002 reagents and I bet you'll see the deep purple color form. The DPD powder (R-0870) used in the TF-100 kit is designed for FC levels all the way up to 50ppm.