For what it's worth, I believe I used 3 bags for my 29gal. Depth is 3" in
back sloping down to 2" in front.

"Giancarlo Podio" wrote in message
m...
I used 5 bags in my 55 gallon. 6 bags plus a large bag of regular
gravel to fill my 90 gallon. Both have a 3-4" deep substrate.

Hope that helps
Giancarlo Podio