hey buds-- yup, a fresh pH reading is in order, and info on your feeds (NPK #'s), dosage, soil brand... brudda Step' makes a good call-- from the looks of things, more than one thing is going on, most likely suspect is off pH, which can make the diagnostic waters more muddied,... the discoloring and patchy necrosis smacks of P defc., the overall yellowing on higher leaves might be tied to it, or could be some S defc. starting too,... If the soil pH is mid- 5's, several nute elements start to get locked out, especially P,... Mg and Ca don't do well either,... How will you be testing? best way is with a quality soil pH probe, like the Accurate 8, otherwise, it's the dubious run-off method, which is generally a faulted one, due to lots of potential measurement error... often folks just take run-off right from the pot base, but that will not give an accurate reading, especially if collected from a dirty saucer! ...here's a link to an improved method and calculation, that helps eliminate inherent sources of error/contamination-- ( https://www.autoflower.org/threads/...-for-run-off-testing-and-ph-estimation.41733/ ) .... we need to find out if you have a simple lack-of type defc. ( probably not if you've been adding PK booster), or a pH lockout causing the nutes to become unavailable, even if present,... or least likely, but not out pending nute info, toxicity issues,....Fe maybe that's what I was thinkin ... Realistically it could be anything until we know if it's acidic or alkaline...forgot to add: nope, Zn is out, no symptom match at all there,... it's very distinct! --it is however, a very common micronutrient defc., along with Fe,... Mn is quite rare,...
...Guys, if you haven't seen it yet, check out the Defc. Pic Depot I put together here, in the sticky's section here, above the general postings section,...
You have a furnace? Use the condensation run off unless it's fixed to the drain pipe. Basicly distilled water@Waira
https://www.autoflower.org/threads/first-auto-indoor-grow.52101/
Link for the grow journal
I should add that my house has well water that has some iron and a bit of sulphur to it. I sometimes get em spring water and hit em with some of that