Platii,
Hi welcome to the forum. I have a little bit of disagreement with some of what you advised.
Usually yellowing lower leaves means that you are lacking of nutes which mean the the 3 main elements N-P-K plus MG not only nitrogen. so I think you need to repot with fresh soil because your soil is losing its
( I will assume you mean buffers)
It could also mean over watering. It could mean many things actually that is why I want the form filled out. We use the hell out of that form here.
There is something u need to pay attention to which is that u r washing off nutes of the soil as u water the plants , in general the nutes in the soil will last between 2 up to 4 weeks.
IF he is over watering. The plant will take 6 weeks to use up what goodies the soil has if you don't over water and wash them all out. Cannabis does not like sopping wet soil at any time unless outdoors in real nature.

I find most problems are created with adding nutes.