you say your testing the run off from the saucer, which i suspect will be encrusted with salt which would give you a false acidic reading, you should catch the run off in a clean saucer, then test
i never test my run off if the plants are doing ok whats the point,
the pictures are crap in that light, its hard to see the color of the leaves, are the leaves at the bottom getting any light ?
some of the leaves at the top are looking a bit MG def, are you letting the pots dry out before watering
they still need N in flower but not as much
i always thought the use of cal/mag was dependant on your waters EC, also canna A/B has cal/mag included, dont give them cal/mag unless they need it, get yourself an EC truncheon and feed them at 1.2EC, with the ratio your feeding at the moment you would be getting around 0.8 -0.9 EC, use...
you dont need perlite
and you do NEED to let the PH fluctuate (5.8-6.3) or you will lock out nutes
looks more like enviroment to me, temps RH, i would leave out the superthrive untill it sorts itself out, everything it needs is in the A/B
heres a chart for ph, some new growers keep there ph...