Quote Originally Posted by Gen
the ph rises due to uptake of CO2. The water is the limiting factor. The plants do not discharge into the water.
Maybe we are not talking about the same thing Gen.

Plants do discharge unused nutrients and by-products back into the water. That is why the PPM is only accurate at the time it's mixed. After a few hours with the plants it will start to change. Another reason why you change your res every 5-10 day's.