420FastBuds

Its normal during the last two weeks plants change color because they are maturing nice plant by the way

Fix ur PH

From ur dairy i can assume that u're underfeeding em (like a lot) everything was fine till the week 5 then they've eaten up all nutritions from the soil so u have exactly NPK+Ca+Mg (and more) deficiencies u should consult with someone how to use ur ferts more properly for next grow soon u'll harvest em so no point to overfeed em now, just give em little more then u did if u planing to let it grow more then 2 week and enjoy whatever u grew

This is potassium deficiency or lock out…that's my opinion The third option can be the poor quality of the water you are watering with, it can have too much chlorine If you use water directly from the tap and do not let it stand, it can be a problem

That looks like calcium issue. If you grow in soil, mostly accures when ph is wrong. Double check ph, meters can lie , make sure you are in good range.