So the water in my overflow keeps rising and falling, I've tried adjusting the airline (removed it completely), and I can't get a steady water level. Running an Ehiem 1260 on my 90 Gallon cube.
I had that problem on my 45 cube. Check your drain line. It might be building up an air pocket which will cause the water level to rise. When the pocket breaks, the water fills the drain line & water level drops. If you have a flexible line move it around until you get a constant flow.