Nice system! I have a CC 4 - 8 gallon unit system that I increased to XL dimensions. Love the system. I have some 13 gallon units and was thinking of doing a system like yours with the 3" bulkhead connectors. How many air stones do you run in each 13 G unit and what size stone? I use two medium gray air stones in each of my 8 gallon units now and have great results.Thanks! It wasn't very difficult for me, but I have a background in plumbing and construction. I'm digging the system so far. I took photos of the entire build if anyone wants more info. I figure I'll do a write up at some point, but am focused on CCO for now.
Again, nice setup!!!