Leaves yellowing

Ok I started this plant on July the 13th in some pro mix and ewc and some happy from 7-4-5 the plant developed very slow at first but has now taken off. But now I am starting to notice some spots on my leaves and also some yellowing on some of my bottom leaves I always make sure to check ph before watering I am watering every 2 to 3 days. And also some of my fan leaves feel very this and kinda brittle. And also some of my stems are purple.

I removed these 2 leaves

Any advice will help thanks in advance

I would really like to know about the brown spots so I can correct it I have did a lot of research and it could be multiple things and I need some advice from an experienced grower

Calmaté.. your going to get some different opinions / options here..are you in flower ? What kinda light/s are you using ? Sometimes it takes longer than an hour or two to get an answer.. good luck

I am using 900 w Phlizon and no I’m in veg