NOw all you have to do, is keep checking your ph and ppm once you fill the rez...top off with water a couple times before you changeout nutes...I don't follow the regimen in a rez like this as much...I let the plants drink the solution...top-off, top-off...then when solution level is just over the pump...I put in fresh batch of nutes...most of the time, I just mix 5 gallons to 10 gallons at a time. I do not always fill rez. later.