Overbuild your plumbing!

This is something I thought I knew when I was upgrading the pond. I knew that the inner diameter of the outflow pipe had to be larger than the inflow pipe, as more water can flow from a pipe under pump pressure than can flow by gravity. I decided that I would go up 1/4-inch from the inflow pipe for any outflow pipe, so when I started building components for the new pond I used 1-inch pipe for all of the gravity flow sections with the intention of using 3/4-inch pipe and hose coming from the pump. What I did not anticipate was that the pump I chose could move a whole lot of water through that 3/4-inch pipe, and overflows ensued. I added a second 1-inch drain line to act as a overflow/filter bypass from the fish tank back to the sump and the problem went away, but at the cost of making the system look overly messy. The take away lesson for me was to use outflow pipe that is a minimum of 1/2-inch larger in diameter than the inflow pipe.