Maybe i'm confused, by why are you adding nutes to ur aero res when it isnt a water change? Remember, water evaporates, but ur nutes wont. So if you continually add nutes when ur water gets low, you could be increasing the nute strength on accident. You need EC/PPM tester to check your PPM to see if you need more/less nutes. Even with that, you dont know how much of each nutes has been eaten and by just adding nutes when the ppm gets low you get ur ratio out of wack. Rule of thumb i use, once i have added 50% of my res in FRESH water, or its been 2 weeks, i change my water. That being said, idk exactly how that little Extra Elite thing works, thats just what i do with my home made aero unit