sump return pump GPH?

And I could even agree that you are right, but I do not think comparing two tanks is how to settle the question. But as far as what you explain is going on I could see that.... especially since even if I can supply a 100% single pass flow path through the sump... once in the skimmer it is all mixed up and certainly not a single pass filter. I think that would be measured by an actual contact ratio of how much water actually contacts air.... meaning we could get our flow properly high, and get our single pass flow through the sump... but if only 20% of the water contacts air in the skimmer itself... then it is a moot point. Just using that as an arbitrary number you would have to turn the tank over 5 times per hour to filter it all.. and of course we know that it would not be every 100 gallons.

I see what you mean, never really thought about it. If the skimmer is only doing 20%,(i DKN, could be 50%-90%) then allowing it to clean what it has 100% you can reduce flow by 5 times and still process the tank.

 

I think I know why I had such a hard time finding out what the general rule is, there isn't one.

Now I just need to figure out what I want to do. I have really liked seeing the three different sides of things.