Look.
I am basically saying the same thing as TipTopToker. Focus on basics of the plant. The difference is that I prefer to include ppms under my defintion of the basics, and he does not. No big deal.
We both have great success....speaking with the benefit of the doubt that I trust what he says, because so many others here do....and I know the success I have had growing COPIOUS amounts of hydroponic weed myself.
We take just take slightly different ways to get there. Myself, I like to have a pen, simply to test the ppm of straight water at my source. And I like to know that I didnt' accidentally brain fart, and toxify my water because I got way too stoned before I went into my room, and mixed my solution wrong.
I like having the tool there for comfort....that is a big factor for me.
That being said, once I got familiar with the strain I had, I had a routine setup, and knew my mixtures. The pen was simply a safety check at that point.
Good luck. TTT is good to have helping you.
DD