I was in the same boat on my new build a few months ago. With my old tank I used my ghl doser to handle the ATO but with the new tank I wanted that dosing head for something else. So I thought about buying the old reliable Tunze 3155 but when I figured for that price I could try the Auto Aqua unit which will take care of my ATO plus give me auto water changes. It was a no brainer and so far I'm really pleasedWas on the verge of investing in a Tunze 3155 but I might have to strongly consider the Auto Aqua instead.