"topping off" the solution?
 

Ron,
What do you mean when you mention "topping off" the solution? I have no idea what it means.
Mike

Topping off means filling up your nutrient solution tank when it gets low. You should add nutrient solution to the water every time you top off to keep the correct PPM. The only exception is to add just water if you want to lower the PPM because you might have put to much nutrient solution in your tank.
Ron