@oscoy, yeah bro invest in a good ph meter. Even with the good ph meter, you have to recalibrate so often. So if you can, get the ph calibrator and go from there.
@MaryJaneUSA, I use a cheap ph meter :/ is it possible I am having a wrong pH? Yes you are right, I was hoping high plants compared with what I have right now. Theorically I have it around 6.2. Thank you for your comment.
I am using a substrat that came ready to start, but they are too small for 7 weeks. I think closet temperature (where hps is) could be affecting it. Thank you for your time.