New tank without a filter (updated with pic)

[ccCapt]

Looks to me like the problem with your skimmer is the bubble difusser box. It's way to high. The top of the box should only be 1" above the surface of the water. I think with that box so high, it's causing back pressure. I have the same skimmer, but it's in my sump.

 

[GuOD]

Looks to me like the problem with your skimmer is the bubble difusser box. It's way to high. The top of the box should only be 1" above the surface of the water. I think with that box so high, it's causing back pressure. I have the same skimmer, but it's in my sump.

I actually tried setting it up many ways when I first got the skimmer (and had the filter running at the same time). My roommate got the 65g model and we both had the same problem. With the diffuser box only 1" above the water surface, the box would overflow almost instantly. I don't know why but the box just doesn't seem to get the water out fast enough. However, when I raised it higher it stopped overflowing and was working perfectly fine.