Ah, I've been wondering about this since the start of this thread. I just couldn't find any info about what the MIOX test strips are doing or how the results are interpreted.

MIOX depend on chlorine for disinfection while chlorine dioxide apparently does not. I was thinking that if the MIOX test strip is calibrated rather high, even fresh MP1 tablets may not generate enough free chlorine to register at all on the test strip, making it impossible to detect any difference between unopened and opened MP1 tablets.