should keep adding water to a reservoir to keep the water level
 

Hi Ron, just wondering if you should keep adding water to a reservoir to keep the water level the same as the plants drink it up or if its ok to just let them drain it down to almost nothing and then just refill it. I've heard that plants use a lot more water that nutrients and if you let the reservoir just drain without refilling it then the concentration of nutrients will be too high, and the plants will get over fertilized. So again, let it drain to the bottom or keep the level constant? Your wisdom is appreciated my friend!

It depends on how much time we are talking about. That's why I don't use to large of a reservoir so the solution gets used up in a few days. That way I'm not tossing out to much. Nutrients can get out of balance with large reservoirs.
When I hear that sucking noise and my plants are screaming feed me that's when I add nutrient mix.