I got 14.5 gallons, or 55 liters.
-FHM
yep spot on I found this place quite handy http/reef.diesyst.com/volcalc/volcalc.html
To be honest I don't have any experience with Under Gravel filters so it's not very fair for me to comment. But based on what I've read / heard, they can be harder to maintain than other filter types. Hopefully someone will help us out with this!
So where abouts are you upto now? Everything set up and running (apart from heater)? Have you tested your water yet? What kind of fish are you thinkin of gettin?