About 6 weeks ago I placed a Finnex refugium on my 40 gallon planted tank. The small pump that comes with it provides a low flow that seems right for a refugium intended to cultivate food organisms.
I put Japanese maple leaves (the finely divided kind) into the partitions and let it "percolate" for about 2 weeks. At that point I added a package of various diapause eggs (moina, etc.). After a week or so I could see tiny dots swimming around in there. The flow seems to be low enough to not wash all of them into the tank which is what I wanted.
I just purchased some scuds and a moina/daphnia/etc. live culture (which will arrive in a few days) and will put these in as well.
Another thing that will go into the refugium are some pink ramshorn snails and some spike tail trumpet snails. A couple of years ago I added some assassin snails to the tank to control a rampant pond snail outbreak and they have done their job a little too well! I want to have some snails in there for my long arm shrimp but don't want to keep buying snails and don't want to set up a separate snail tank so we'll see how this works.
I figure I can scoop out snails into the main tank from time to time, and also stir up the water in the refugium to flush out some of the smaller critters.
The refugium is not lighted at this point, something I might consider in the future but not for right now.
So, currently the only "media" in the refugium is the Japanese maple leaves. Should I add some gravel or sand, do you think? And if so, which would be better? Of course I could always put sand in one part and gravel in another and see how things turn out!