Running Stealth Hydro Bubbleponics system. Anytime it needs water (usually daily at this point in flower) it's ph'd and nuted up.
Yo ray... I'm the same man. As mostly crazy that is.... My rez is about 28 gallons full.... I have never once let it get lower than 24 gallons. My plants drink about a gallon a day (total), so every other day (about) I add 2 gallons. I usually don't need to pH it becuase my rez is so big (it doesn't fluctuate much). Depending on how lazy I am I add the appropriate amount of nutes to the 2 gal top off. And I completely change the water every 7-8 days. (lots of nutes I use)
With your smaller rez, I would add the appropriate ammount of nutes each time as the ppm would plummet without.
What you might want to do, if it makes sense for you is make enough nute mix for a week at a time, then just top off from that. Do you see what I'm saying?
I'd do it with my setup, but I'd need to keep an extra 10-12 gallons somewhere and that is a lot of space.
I hope this makes sense. Let us know if you have any other questions.
One thing is for sure... I suggest you never let the rez get below halfway. I don't know if it makes a difference or not, but I wouldn't do it.