k-1000 to DPD test Huge disparity

[bob27nli]

Testing for chlorine and getting a big discrepancy between the K-1000 chlorine reading and the one from TFT kit with DPD powder. The DPD powder is a new container, so I not suspected a problem with it. The K-1000 is reading 3-6, while the more accurate DPD is reading .5 for free chlorine and .5 for CC. Using the .05g scoop that came with the TFT kit to put the "heaping" scoop in the 10ml of water and following the rest of the directions...

This is my second year doing my pool using TFT methodology. I opened the pool two weeks ago. Its heated at 88 degrees, rest of my readings are Ph 7.6, TA 100, CYA 30 and borate 50. I have co0nditioner in two socks in the skimmers to bring the CYA up. Borate tested at 50 when pool opened so did not add any this season (yet). I only use liquid bleach for chlorination. Use solar cover at night.

Last year my pool was crystal clear all season. Now, it's not completely clear in the deep end, and I have soap bubbles on the surface, really noticeable when I run the waterfall.

Any ideas????

 

[jblizzle]

How old is the K-1000? Or is it the one included in the TF-100?

 

[bob27nli]

The K-1000 was part of the TF-100 which I purchased last year. What I have learned since posting by reading the Extending Test Kit Direction is that
" The exact amount of R-0870 powder used is not critical. The goal is to add more than you really need rather than using too little. Using too little R-0870 powder can throw off the results of the test. You need to use enough to bind to all of the chlorine that is present. Adding extra, within reason, has no effect. At very high FC levels it is likely that you will need to use more than the normal amount."

So I added two level scoops and the disparity is closer, get a 4-6 on the K-1000 and a 2.5 FC in the DPD but this time with 0 for CC.

Still a fairly large difference but within tolerance.

I'm guessing the clarity may be that I need to bring the chlorine up a tad more, especially with all of the tree pollen coming down.

 

[jblizzle]

Trust the FAS-DPD results ... the OTO is too subjective

 

[duraleigh]

We always advise people to use the K-1000 (OTO) chlorine test simply to check for the PRESENCE of chlorine.....it's just too subjective to be very accurate. (however, it is very dependable, just not accurate)

When you need precision, use the FAS/DPD and trust it.

 

[JoyfulNoise]

When I do an OTO test, every water sample from 2ppm FC to 8ppm FC looks like the same shade of yellow to me. Then when it's over 8ppm, I start to see the Orange-brown color. Anything over 10ppm makes my OTO go completely brown and curdled like spoiled milk.

So, yeah, for me I only use OTO to make sure I've got FC.


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[bob27nli]

Yes, will only trust the FAS-DPD results going forward. Adding more chlorine based on that readi.

Also, change the pool return jets so they are now pushing toward the surface and creating surface water currents. Seems to have helped with all the pollen and the clarity of the pool water on the deep end is back! :grin::grin: