When i set up my 90 gal system i included a gravity fed ATO system. I meticulously worked the math and calculated the top of the sump. started the system and, yes, my calculations were correct. I ran a water line from an elevated reservoir to a float valve on the water line of the sump. THEORETICALLY when the water dropped below that line so would the ballcock, opening the valve, and feeding fresh RO/DI water into the system. Sounds good, right? And it would have been great if only the float valve hadn't been defective. My reservoir is 30 gallons and i have found it soaked into my carpet twice before my troubleshooting detected the bad valve. Lesson learned: Check these things before you turn on the water. So, Tunze folks, I need this Osmolator!