Harvest Advice & Magnesium/Calcium deficiency

Hi everyone,

This is my first time here, also this is my first ever grow.

I have two plants, separated by 2 weeks (Jack Herer Autos). Yesterday I noticed that the newer plant had some rust markings on 2 fan leaves, so I ordered a soil PH tester just to make sure that I'm dealing with a deficiency. However, I went back to check on them this morning, and noticed that the top of the main cola has gone brown over night, as it appears that also some of the trichomes have suddenly gone amber, but I'm not sure. (Also, I did find a dead butterfly next to the plant, so maybe she crashed into her and spread some bits everywhere??)

Should I just harvest these top buds, and then start to treat the rest of the plant?

I've attached some images. The resolution should be quite high, so you should be able to zoom in.

Any advice would be really welcome, thanks!

This looks like week four - nowhere near ready to harvest.

Dont try and mess with soils ph, just give ferts water and step away till it needs them again.

You will get no where adding extra cal mag if its already in your ferts and even more so for soil.

Understood, thanks for the reply, much appreciated. And yes, spot on with the timing, this is week 4 of flowering!

Also, I used a soil that claimed to have 4 months of feed mixed in it already (Westland Gro-Sure), so I've been cautious to not add any more ferts. Do you think I should?

Thanks again!