With the brand new DPD kit from Leslie's (store replacement for my expired Spanish one), I tested my bromine spa a few minutes after activating with MPS.
The reading initially indicated lower than expected (based on an OTO test I had just done on the same sample), but slowly (over a few minutes) got darker and darker until it settled down about a notch (2 ppm) higher than the OTO test.
I read that MPS can throw off the DPD's free chlorine test; can it affect the total chlorine/bromine test? If not, why don't my tests agree?
And what's up with the indication creeping up? Is that normal? I've read that darkening OTO usually indicates CC, but this is DPD.