Ph low. Advice on up!

Hello folks. I just recently tested the runoff of 3 of my girls. Ph in was 6.4. Runoff 5.0. Ok so on my next watering what should my ph be going in to get in range? 7 gallon ff sf hf and of mix. I noticed that my ppm was not adjusting between watering. This explains. Ph low! I have a blue labs soil/h20 pen arriving today! I figured i would upgrade to a 2in1 pen! Thanks folks!

Low pH is often the result of a salt buildup. How long have you been feeding the plant nutrients? WHat brand of nutes are you using?

I have only fed ro water with cal mag at 200 ppm 2x. Week 4 veg!

Ff trio along with cal mag. Great white used during transplant. Oh yeah also adding silica also with cal mag.