Ph low?

i agree probably not the ph , but you can check the runoff to be sure... brownish looking rusty yellowing drying out leaves during early to mid flower usually is an indicator of the plant does not have sufficient calmag levels but if you notice the leaves effected start with the lower ones that leans toward nitrogen...with that said those rusty spots i think tell the story... good luck

I think this might be a potassium deficiency, but it’s hard to say for sure. Check the pH levels (5.5–6.0). Are you adding Cal-Mag?

6.5 is at the sweet end of the range. So even if this is not the problem take it down to at least 6.0 and not less than 5.5. Alright the photos. The fan leaf believe it or not is probably phosphorous. Did you add more of it a week or so before the photo? Did you cut back on nitrogen since you are in flower? The right photo is pale.

Reminds more like lockout or root issue. Cause either overfeeding or wrong watering habbits, that could lead to pot ph drift. In diary plants look too heavy stripped and light is just bombarding them, lift it higher. You use dutch buckets, when plant would be ready for watering , i would just pull it out from pot, if all roots are brown - you have an answer. At same time you can check how to measure and collect run off. Its values will tell you even more ;))))