CO2 Diffuser Position

I would try to position it nearest to the outflow of your filter where the current is the greatest so the gas has a better chance of being dispersed throughout the tank.

A place where it will be in the flow of water and distributed through the tank. Where that is in your tank, I do not know.

I place them directly under the HOB outflow sitting right next to the intake strainer. This way the bubble streams get split by some going into the intake and others being dispursed by the outflow. Believe it or not, I have actually found this to be working better than when I had them sitting directly below the intake where a vast majority of the bubbles were being taken up by the intake.

Yeap this is what I have to do this weekend..Mine is on the far right of my tank, and I am going to position it smack dab in the middle.

As everyone said, best place is directly under the overflow of the filter. But i would also make sure it is at the lowest point in the tank that way the bubbles have more time to diffuse.