No one ever said of any element in an aquatic system "Gee I wish it were smaller".
It's the 625 gal 8 ft. x 2 ft. from tractor supply (https://www.tractorsupply.com/tsc/product/round-plastic-stock-tank-8-ft-x-2-ft) ... which now costs $699?! I think I paid $280 for it. You only need 12 inches of gravel above the pipes though so this thing is oversized height wise
Discussion
For sure. I wish I'd used a 10ft poly tank, one of those gray ones