So the TF-100 has both the FAS-DPD and the OTO chlorine tests. The pool shop sold me a Taylor K1001 DPD test kit before I found this forum. I'm getting my new SWCG dialed in so I'm carefully testing FC daily to figure out where to set it.
Out of curiosity only, I've been running all three chlorine tests daily and comparing the results. Here are this morning's results:
FAS-DPD = 5.5
OTO = 5.0
DPD = 3.0
These results have been fairly typical over the last several days with the pool store's DPD test always showing about 2.0 less than the OTO or FAS-DPD tests. I expect that the FAS-DPD is the most accurate. OTO and DPD can be more difficult with color matching. I don't think the DPD should differ from the other two tests by that much. This difference has also been very consistent across 5+ days. Had I been relying on the DPD only there would bee too much chlorine in the pool. I'm pretty sure I'm running each test correctly. What gives? Old chemicals in the DPD?