Got a few more questions that you folks will likely be able to shed light on. I have to the pool in a good balance. I have been testing TC with OTO daily during the week and then once a week I do a FAS-DPD for FC and CC. On the days I do FAS-DPD, I also do a OTO to compare. This is where the mystery starts. I notice that OTO is consistently lower than the FC from the FAS-DPD. Yes, I realise that OTO is testing TC and FAS-DPD is testing FC. However, the OTO results should be the same or higher than FAS-DPD. Now, I have read the extended instructions (thanks Jason) and noticed that OTO is not accurate above 2ppm (> 1ppm). But there seems to be a consistent low bias versus the FAS-DPD.
My other issue is one of color matching. I use the OTO to test during the week because of the convenience factor. The pool is in balance so testing with FAS-DPD once a week to test both FC and CC and using OTO to keep tabs during the week seems logical to me. I run a CYA level of 60 and as such my target FC level is ~4. The 3-4 range is precisely the two colors on the OTO that are nearly identical. It is so difficult to tell the difference. Given that your target chlorine level is so critical, I am hesitant to use the OTO for an extended period without FAS-DPD
BTW - I use a Taylor K-1000 for OTO and TF-100 for FAS-DPD
Okay here is goes
1) Am I crazy, or do others find that OTO always comes in lower than FC in FAS-DPD??
2) I want an easy way to keep tabs in chlorine daily, and keep FAS-DPD for periodic checks. Are there better ways than OTO (or the K-1000)?