Great thread...lots of cool photos and interesting bits of information.
Thanks for taking a look!
I understand the ceramic rings (like Fluval SPEC biomax??) are the biological filter and the foam is the mechanical filter? What kind of foam did you use?
In a nutshell, yep! I'm using Aquaclear Biomax (70g-size) and a small bag of some other brand, but it's all basically the same thing. The porous ceramic provides lots of surface area for bacterial colonization, which in turn helps to break down waste. I'm using two bags of ceramic rings; one in the first chamber and one hidden in the bottom cavity of the second chamber - the first bag provides some mechanical filtration, the second is simply additional surface space for bacterial growth.
In the first chamber both the rings/foam help to physically trap waste, but honestly most of my mechanical filtration comes from water changes; I still do a 50% WC every 36-48 hours and siphon out any visible detritus from the substrate / filter chamber. Ammonia/Nitrate/Nitrite are all virtually nonexistent but I still keep up with the WC's - I could sit here and list all the reasons why, but it boils down to a simple principal: there's no substitute for the benefits that regular maintenance / water changes provide to a tank.
Also, in your case it's not too late to modify the chamber if you want to go that route! Sure it requires some effort, but if it's something you're interested in doing then don't let some extra work get in your way
I found the drilling to be very easy and had it drilled / cleaned / ready to use in less than 10 minutes. Best of luck to you!