I've been running a test, where I have my base nutrient(Flora Nova Bloom) in a reservoir diluted at full strength. I keep it bubbling with an air stone. It takes me about a month to use up the 27 gallon res and my ph and ec remain the same the entire time.
So that will meen that not alot of water evaporated in that time, right? I would think the constant bubbling will affect the ec, since the water evaporates..