Day 56 flowering leaves brown

[Deadhead91]

You could go with this it's as simple as it gets
General Hydroponics pH Control Kit https://www.amazon.com/dp/B000BNKWZY/ref=cm_sw_r_cp_apa_jGFKAbG9DT674

And reverse osmosis is the best with plants

 

[Waltermelon]

Your friend is right. You can back those lights up a bit and get better results. You can also throw in some cal-mag/ Epsom salt to help with those leaves that haven't died yet.