Ok...
That's reclaim water, it's coming from the units that remove moisture from the air. If the room is sealed, there's nowhere else for all that transpired water to go, right?
So, into the barrel it goes. But since it's been transpired, it's pure water. Hence EC 0.0 on the meter. So why not mix your nutes into THAT? Damn straight, that's why there's two cans; the reclaim water drains into one while the other holds the nutrient solution. Use up the nutes and strangely enough, the other barrel is full and ready.
CLOSED LOOP. You not only don't need an RO filter, you barely even need to add water at all.
I add dry nutrient salts, very easy to do in such soft water.
I add co2 in the form of tanks, monitor, controller and regulator.
Sealed room agriculture is pretty nifty. Who knew?