
Hey
Moon-- those skinny probe type meters are notoriously inaccurate, I have tried a few makes, and none work well enough to rely on... the Accurate 8 operates on the same principle, but is more robustly built and better calibrated,....BTW, they are only for in-soil testing, never liquids! You'll still need a pH meter for measuring pH in solutions,...be sure to get calibration solutions for it, and storage too,...
....misting is fine, and RO is best, as long as the RH in there isn't too high to begin with,... Now, I'm am outdoor grower mainly, so my lighting skills aren't great, but 1000w in a tent that size is near overkill! CFL are utterly redundant,... In fact, what are you Temp's and RH in there? That light is a damn furnace for heat output! .... Definitely, use Ca-Mg when using RO water; there's no CaCO3 in there, either to buffer pH or add Ca++ for the plants,...
.... harsh diagnosis brother

.. we have several MS folks here,... one cat you should look up is Eyes of Fire, an excellent organic grower, and dude is a total gas!
.... HF OF, it's all a gamble it seems,.. some folks get okay bags, others get shwagg! I tested, with the A8, 4 bags of both OF and HF at two different shops, different times,... all tested in the low 5's pH!!

--- that is instant FUBAR,...so, beware!