how often do i need to add nutrients to my plants water in a soil grow. certainly not every time? i don't have any sort of fancy gizmo's like a ppm meter or anything, nor can i afford one right now. all i have to check the pH is a liquid tester that i'll test the runoff with. so, that being said, any way for me to check the nutrient levels? or will i just have to guesswork it and look for signs of the nutrients being too low/high on my plants?