how many times a hour should the water go through the sump?
 

just wondering how many times an hour should the tank water go through the sump? 1? 5? 10?

I would aim for about 3-5x per hour.

If you have selected the correct skimmer and the flow in the tank is moving the water towards the overflow box then.. 2 or 2 1/2 times max.

There is really no set amount, slow or fast both work the same. Mine is set at about 800GPH swap over or almost 5 complete tank volumes.

Why a max of 2?

Actually skimmers work best at a 1 times turnover, that's how they are designed, beyond that they become less efficient.

I was waiting for someone to make this argument, please explain to me why that would be?

If a skimmer draws in water @ a set rate which is completely unrelated to the water movement around it then why would slowing that water down increase its efficiency?
Levi

It's quite simple, if you run a lower turnover rate the water(containing surfactants) coming from the overflow box is concentrated rather than being 10% crap and 90% water in a 10x rate, the skimmer does a far more effective job with a concentrated solution than a diluted one.

By that logic, the same amount of water would pass through the skimmer would it not?

Theoretically:
1gph=100% skimmed
10gph= 10%/gal

I dont really have a preference. As long as water gets skimmed its a win situation.

If you skim it 100% then what you return to the tank is clean, if you skim 10% of it then 90% of what you return is dirty or unskimmed, why would you do that when it costs more money in hydro and pumps to do worse?

I understand that. But say, someone was using there return pump for extra flow to their tank. The extra water movement through there wouldn't technically affect the skim-mate that is pulled out of the water.

That being said, there is no actual way to test out these theories as a skimmer pulls out skim-mate in both situations. This test would be almost impossible because everyones tank (or say a "test tank") would differ from one another so getting a control would be practically impossible. I am not saying your opinion is wrong/invalid , I am just saying that in my opinion the flow rate through your sump isn't a big thing to lose sleep on.