Quote Originally Posted by PoolDoc View Post
It goes to 10, nominally. But 9 of 10 people cannot distinguish a 5 ppm FC level from a 10 ppm FC level, using that kit. Diluted, you're adding additional error, so now you can't distinguish 7 ppm from 25 ppm!

Additionally, if the FC = ~15 - 20, you'll read maybe 2 - 5 ppm. If the FC > 25 ppm, you'll read FC=0. Very *experienced* pool operators can recognize those errors . . . but then we don't deal with very experienced pool operators. Put plainly, DPD color match testing is INFERIOR in accuracy, and VERY INFERIOR in reliablity, to OTO tests.

Many of the criticisms of OTO testing seem to have originated as a sales ploy by Palintest, back in the day when the DPD test was still patented and very profitable.

Pool owners with K2005 kits need to buy (a) a cheap OTO kit (quick & bomb proof -- if not very accurate -- chlorine testing to 50 ppm) and (b) a K1515 DPD-FAS add-on (accurate FC testing to 50 ppm).
May be I the 1 in 10 but I can tell the difference and the only time I have gotten a reading in the last of 0 was before I added anything to the water. Diluted the max reading you can get is 20 at least according to instructions on the box cover. With the amount of bleach I used to clear up my swamp I pretty sure I was way over that and never bleached out. I am assuming by bleach out you mean it goes clear which would be a reading of 0 ppm. I only say this because my results over the week seem to contradict what your saying. Either I am screwing up the test pretty bad or something has changed with their kit.

On a side note I have been keeping reef tanks for almost 20 years so I am pretty good with test kits as we had to test same things with the exception of CYA and Chlorine and a few things we are not concerned with in a pool.

Why do you recommend both an OTO and a DPD-FAS test kit for chlorine seems redundant if they both test the something or am I missing something.