Overfert, and use potting soil next time. Don't feed so much. Maybe raise the lights some to get it to grow taller. 5.2 is a little too low, even for what appears to largely be a hydro grow. Just potting soil and you won't have to worry about pH anymore. If you want to stick with perlite, pH around 5.7 should be fine, but it will fluctuate. Look more at your ppm and determine if pH is rising because ppm is dropping. If so, probably need more fert and keep an eye on that. Soil is an easier thing to do.