Still have yellowing/drying/dying leaves at bottom of plants. Is this normal?

Some of these leaves consist of drying up and dying, some yellowing. My plants are huge now and I expect that some of it is due to lack of light penetrating the canopy, therefore the lower leaves do not have sufficient light; correct? Furthermore, I believe some of this may have been caused due to my ph levels. Although they have consisted within the region of 5.8 - 6.4, I have chosen to flush with a 5.9-6.0 solution of water over the past 3 days. I hope what I have done is right just incase my ph were of inequal levels. I also believe that due to the weather in my country being extremely hot over the past month or so, degree's have risen to as much as 105 degree's farenheit. I know this is terrible, but there is nothing that I am able to do in order to lower the temperature. Luckily, my country is beginning to go back to normal weather so things should only get better! I would like an opinion from several people in order to justify what I should do to fix this issue. I decided to move to flowering stage yesterday. All plants show signs of maturity (internodes not on same level and all female sex shown) so I don't see why I shouldn't have started; right? Lastly, one of my plants has always been lacking in growth overall due to poor care at the beginning (rookie mistakes) but it has come back to its poor quality again. Some leaves show brown spots and some at the TOP are yellowing overall. I would really appreciate some help. Thank you. (Apologies for quality of picture(s)).

I hope there is sufficient evidence for you to work off of. Please help! I have also fed magnesium to each plant as I believe it could possibly be mg defiency?

Try your ph more towards 5.5 I do see some ph inconsistency also see heat stress too as you mentioned, hopefully it will cool down for yas. Also make sure to not let the grow cubes get too dry before you water again.

Thank you. It's been almost completely successful up until now. Much appreciated!

I feed in at full strength with advanced nutes so once the first onset of flowers start (bout week 2) I feed in at half strength. By the time I do the half strength the plant has enough food built up that the half strength feed allows it to consume what's on board and is ready for a good feeding after. Ill repeat this a few times during flower to prevent build up. Plant depending.

Just keep at it soon enough the experience will come and you'll be able to combat what comes at you with ease.

Ahh! That's very interesting. I'm intrigued to know what the results come out as for you if you do not do this compared to your preference as mentioned. People such as yourself inspire me to tend to plants with care and emotion. It's not a factory, it's a bondage between man and plant.