I would check my runoff and compare it to a sample of the soil i can take from the top and find a balance to see if something is really off with regards to ph or ppm in my medium. If the results seem reasonable..i would water it with 2.5L of water WHEN the medium is dry enough with only epsom salt (1/4 teaspoon). See how it responds. I follow my plants so close now, that i do my best to make sure there are no issues except lack of food once i get to flower. At the start i'd be chasing my tail and yield/quality would be affected. Less is more
on my first grow i followed it too much and starved the shit out of my two plants! lol..but after a few years and much gained knowledge, i agree..less is more..because once you go too much of something...it's hard to get it out/neutralize it's affects..especially in flower!