So the surface scum on my 75 gallon was getting a little out of hand. Actually, scum in general is worse than I would like it, but one thing at a time. I whipped this up from stuff I had lying around and it worked like a charm. 20 minute build time and probably 30 minutes to clean all the froth and oil slick from the surface. I'm sure other people have done this, but I couldn't turn it up searching the forum so I'm posting it.
I threaded a 3/4" MPT hose barb into the bottom of a 32 oz deli cup. Inside the cup, I stuck a strainer on the end of the fitting, and filled the bottom third of the cup with poly floss. The barb goes into a scrap of 3/4" hose, and the hose onto the intake of a maxijet 400. I stuck a scrap of 1/2" tube on the MJ outlet to divert the flow, and a suction cup holds the rim of the deli cup in place.
Once I got it in the tank and running, I adjusted the position of the cup until I had just enough water spilling into the cup to keep a constant level inside it - too much and it overflows and releases all the collected scum, too little and it runs dry. I ran it for a few hours, then turned off the pump and quickly lifted out the cup before it overflowed.
Is anyone else using something like this to clean up their tank? I think a maxijet powered gravel vacuum would be a nice sister project.
Full shot of the assembly sucking a little air:
Cup angled just right to balance water flow: