EQ, is the T and RH% still way off like before? This can lead to a variety of problems, most of which are linked to reduced transpiration rates causes by such off env. parameters, not necessarily a nutrient issue
per se,.... Look up in the Reference section for the VPD (vapor pressure deficit) article, and read that, this will explain what I mean in better detail,... overly high T and low RH% can make the plant close up the stomata, stopping the flow of of water/nutes from roots up,... this is to prevent excessive water loss,... Too high RH% regardless of T will make the water evaporate poorly, slowing the "draw" even if stomata are fully open,... Any of this can cause a temporary and sudden showing of nute defc.'s even if they are present... mobile nutes can be draw from leaves, at an energy cost, bit poorly/immobile nutes can't, and that will show in uppermost growth quickly as well,... Until that gets dialed in, nothing will really help, even foliar will be reduced in effectiveness,...
Symptoms look like a micronute defc. for sure, yeah likely Zn, but S and Fe are possibles, the latter least likely because typically Fe defc. yellows from the "palms" outward,... So the question is if this is caused by the T/RH% VPD thing, a simple lack-of, a pH lockout, or if you have a sort ot toxicity lockout where one nute in excess causes other(s) to have uptake issues... Zn and Fe will lock out when in-pot pH gets to about 7.0, S will under overly acidic pH.... Too much P can interfere with availability uptake of a few metal micro's like Fe and Zn....
That MMB is very powerful stuff, and I think too much P might be behind this, pending info on T/RH%, in-pot pH,... but feeding it every time you water may be too much cumulatively, even if the tips aren't showing burn,... Not to say this can't be caused by more than one thing! I advise getting a TDS or EC meter and monitoring the input values especially with MMB,... get an Accurate 8 soil pH probe for in-pot pH, run-off is bollocks for pH testing,... :smoking:
