Hi,
Big Mombasa...like this one :
http://www.petsforum.com/fishnchips/1999/fnc1199.html
Well...it isn't so hot for a nominally loaded 70 gallon tank. It would probably work well on a loaded 20...but not on a 70. Even with an airstone modification and better pump, you might be able to squeeze a 33...that's about it. Sorry. :(
The problem is the reaction chamber (the portion of the skimmer that has the air bubble / water contact) is very short and narrow. The key here is...larger air/water contact volume. Something like a Red Sea Berlin skimmer (I think there is a used one on the board) should probably be sufficient for your tank. If you want to build your own, you can either try a becket type skimmer (lots of plans on the net) or a counter-current (CC) skimmer (Snailman's skimmer on RC). A good skimmer will save you from having headaches in the future.
I have a 90 and I use a CC skimmer -- its about 6 feet tall and 4inches in diameter. [img]smile.gif[/img] The total cost of the skimmer came to about $200 and it skims like a dream.
Hope that helps.
- Victor.