OK... I was starting to have an issue with surface scum on my tank. Powerheads toward the surface just weren't cutting it. Not sure if it was the increased bioload, old lights, or just a combo of everything. But... I found something that nipped it in the butt great.
I've got a Remora Pro skimmer with a Mag3 pump on my 46g tank. I originally bought the surface skimmer that AquaC makes, but it was too big and had several flaws that I didn't like, so it never went in the tank. I tried replumbing the inlet of the Mag3 pump with an elbow coming out of the pump inlet and sending the intake strainer up towards the surface. No luck. But here's the cat's meow...
Get yourself a Tom Aquatics surface skimmer, like this:
... and plumb it into your Mag3 like this:
To do this, go to wherever you can buy underground sprinkler supplies (I went to Lowe's) and get yourself an elbow that's 1/2 male NPT on one end, and 1/2" barbed nipple for sprinkler flex pipe on the other. It's a black plastic fitting.
Screw that fitting into the outlet of the Mag3 pump. Point the barbed outlet of the fitting down. Now take the little elbow thingy that came with the Surface Skimmer and push the smaller end of it onto the barbed fitting. Point the larger end of the elbow thingy away from your Mag3 pump. (See picture above.) Now attach the inlet of the Surface Skimmer to the larger end of the elbow thingy, and voila - nice, compact surface skimmer.
You don't end up using the suction cup clip for the Surface Skimmer as it's supported just fine by the rigid elbows. And assuming you keep your water level pretty close to the top of your tank, the "float" within the surface skimmer should be right about in the right place.
The only tricky thing to this is adjusting the flow. The little "rod" that sticks out the top of the surface skimmer rotates, to raise or lower a little "shelf" that adjusts the intake flow between the surface portion and the lower intake. Play with it a little before it goes into your tank and you'll understand what it's doing. When you start your Mag3 pump back up, have the flow so that the lower intake is totally opened. (Screw the little rod clockwise until it's almost falling out the bottom.) Slowly turn the rod so that you raise the little shelf. You'll start to see the "float" part of the surface skimmer start to go down as water starts to come into it. Keep adjusting until you get the flow coming down from the top float fairly consistently. If you turn it to much, and divert too much flow coming from the surface, the surface skimmer won't be able to keep up with the Mag3 pump and it will cavitate the pump. Not good. Don't do that. You'll know it when it happens as it will make a bad noise. Doing that for more than a second could damage your pump, so be careful.
After a bit of tweaking, you'll figure out where the flow needs to be set at. You don't need much being pulled in from the surface. I had what I considered a "trickle" coming from the surface, but within 5 minutes, every bit of surface scum was gone. Completely.
I'm a happy camper.