A cheap water/fert monitor.

I'm not a hydro grower, but just heard about an old fish farm monitoring trick. When you have your water/fert mixture perfect, put a piece of PVC pipe to the bottom of holding tank, and mentally gauge where the spot is where you cannot see the pipe any longer. Mark that pipe at that exact area. Every few days, put in water. If you clearly see the mark, add ferts. If you cannot see the mark, add water. It's like the dime in a cup of coffee. If you can clearly see the dime, the coffee is too weak. If you can't see it at all, it's too strong. Barely seeing it is the perfect blend. Hope this helped.
One day I want to do a fish/plant garden.