Please Explain Sump Flow = Skimmer Flow for best skimmer performance.

I am hearing conflicting opinions on sump flow rate. Some are saying to match to skimmer processing rate and others say up to 5X tank volume. I have also heard that for a Bare Bottom you want 10X or more.

Lets examine a skimmer in the sump and the inlet and outlet in the same chamber. The faster the flow through the sump, the higher the concentration of bad stuff at the inlet of the skimmer. This can be proven pretty simple by the following; If you take the sump flow to an extremely high rate, the inlet to the skimmer will be at the same concentration as the tank, being the highest in the system. To the contrary if I drop the sump flow to a trickle, the inlet to the skimmer will be clean due to it being processed over and over. In other words the higher the sump flow rate the less the amount of water is passed through the skimmer multiple times.

On the other hand if you are allowing the surface water to overflow into the sump then the highest concentration of bad stuff may in that layer. Therefore if you slow the sump flow the concentration of bad stuff will be higher than the average concentration in the tank. Less bulk water is taken to sump compared to the high concentration surface water.

I am guessing that matching the sump flow to the skimmer flow is a good balance between these two extremes.