Here is a pic of a Hagen Aqua Clear surface skimmer added to a Aqua Clear 70 hob power filter. The AC 70 uses the same diameter pickup tube as the AC110 model. This skimmer comes with an adapter to fit the larger 1" diameter pickup tubes or the 1/2 or the 5/8" diameter pickup tubes. YOu remove the original pickup tube and replace it with the tube adapter that is then attached to the flex hose supplied with the skimmer (A in the pic). Off this tube is an outlet with a flex hose attached. It is routed to the original U tube where you removed the pickup tube from or if its another brand of filter you may need to cut the intake tube and use the adpater.
The new surface skimmer pickup tube (B) has a rod that is attached to a disk at the very bottom of the tube, where there is an inlet or strainer just like most pickup tubes have. It is mounted on the tank wall by way of suction cups that actually stay put, and has a snap in mount so you can pull the tube (B) off the mount and not deal with the suction cups. YOu turn the rod located in the new pickup tube to close off or open up the strainer at bottom of the new pickup tube, so you can divide the suction between it and the floating skimmer part C. The rod that you use to adjust extends up through the floating skimmer head C so its accessible to adjust without a need to get your hands in the water, and also acts like a guide rod to hold the floating skimmer head in place. There is a hollow space under this floating skimmer head that traps air as you place it over the guide rod and into the new pickup tubes top end. This allows it to float and go up and down as water levels change in the tank due to evaporation. You can adjust it for a good full suction on the top, or a slight. I find a slight suction will keep uyp with most tanks once initial film has been removed and works just fine, so most of the suction is then diverted to the lower intake strainer at the tubes bottom just like a regular pickup tube works. For thre price its hard to beat, and my surface water is spotless. Adjusted right, they are relatively quiet, and you have to pay attention to hear it. It may or may not work on all filters, as the filter needs to have good suction, which aqua clears are noted for. The only difference betweenthis surface skimmer and the Eheim model is the Ehiem only comes with an adapter to fit a 1/2" diam pickup tube whereas the Aqua clear model has an adpater to fit 1/2 as well as 1" diameter pickup tubes. I have run this surface skimmer of an Aqua Clear AC20 MINI. I adjust it so most suction is diverted to the skimmer portion of the pickup tube, and use filter bat in the filter itself, and its does a super job of removing surface scum, catching it as well as providing additional circulation. YOu can get a AC 20 MIni for about $12 so for under $20 bucks you can have a power surface skimmer on any sized tank that will do the job, or add it to an exisiting filter. I used to run them in my 2 gala pico tanks until I built my own skimmers. IN the pic you can see the actual water level on the filters U tube portion and the rest of the stuff above is just a reflection of whats under the water, so its not as large as it appears to be overall.