My ato fills up about a 20 gallon section of a 49 gallon sump. I don’t use a pump with my ato. Like I said above, I have a solenoid that the ato controls with a line connected directly to my home’s waterline.
For a tank your size I would honestly look at the Auto Aqua Smart ATO. I have a ten gallon reef and it is perfect for reefs under 30. Really simplistic setup that comes with everything but the reservoir. I just keep a 5 gallon bucket filled with RO under my stand and I couldn't be happier with it. The system was really easy to setup and has run flawlessly since December. Here's the link to it on amazon: https://www.amazon.com/Smart-ATO-Mic.../dp/B0195D3LC6
2015 AA Fantasy Football Champion