YOu dont need to get as scientific as in calculating the amount of water after displcement. The 1
rate is usually calculated on tank capacity empty. The reason is that each tank has its set dimentions that you have to flow the water over.
is just a good average number. I myself have close to 15X and I could use some additional flow in spots. The key is to balance the flow with what you want to keep. If you have a bunch of corals that need high flow then 2
would be better for them than 1
. But at the same time you dont want the current beating on them.
Flow should not be confused with intensity of the current.