On my big tank, I have a huge problem with surface scum, even if I lift my outflow pipes out of the water so it creates ripples. I was scooping it out with stainer, soaking it up with paper towels, but it just kept coming back.
I decided I needed a surface skimmer, but the ones that are available commercially are pretty ugly and very conspicuous, especially when all the equipment in the tank is glassware.
I decided I'd try to build my own.
This is the basic idea, there would be a acrylic tube attached to the intake of the canister filter. It would have slits cut into the top which would act like an over flow on a sump set up. Surface scum would flow down the tube and then get sucked up into the filter.
The blue lines is the path of water flow
Parts I got from tap plastics. 1 inch outer diameter tube, that little circle/half ball thing is to plug up the bottom of the tube, and a special acrylic double-sided tape to bond acrylic to glass. The tube and half ball thing cost about $2.50, the tape was the most expensive at $15 for 20 feet, I ended up using about 10 inches of it.
Used a dremel tool to cut slits into the top of the acrylic tube. I know it doesn't look too good, but it's clear, and it's at the back of my tank so it's not noticeable I taped the half ball to the bottom of the tube to seal it up.
Here it is in tank, it seems to be working as i can notice a small water fall into the tube. We'll see if my surface scum comes back. Sorry I didn't take a picture of it before I put it into the tank, I was too excited to try it out.
I used the tape to attach the tube to the intake pipe and let it set. I wish I took pictures of it but it's in the tank now.
It was really easy to build and if it works, I suggest you all try it out if you have problems with surface skimming.
The only issues I foresee is keeping it clean, since I'm sure it'll get the brown gunk, but I'll deal with that when the time comes.
Also, since the slits are only about 3-4 mm underwater, I'm going to have to be fairly diligent about keeping the water level up. My tank has a lot of evaporation being open top, so I can see that if I let the water level fall below that of the skimmer slits, I run the risk of burning out my filter.
I think the commercially available skimmers have a floating overflow that rises and falls with the water level.