There are also TDS, PPM And EC meters. I understand a bit about them but i dont know the different from PPM and TDS. I think EC test the electrical Conductivity. I am guessing the more nutrients the more EC?
These are old pictures of my room for growth. The led ballest burned. I bought a super cheap, this time fired. When its work is great. Ive never seen a green plant, they are in my leadership. Do you have expensive. Must do your research.