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That's what I said only in different words. Not to kick a dead horse, but the skimmer controls its own rate of flow through the body of the skimmer. In which case slower is better for extracting surfactants, but only within the skimmer itself. The higher the contact time between the water and the bubbles, the more effective the skimmer is at pulling out waste. This has nothing to do with the rate of flow through the sump, tank, fuge etc.

Find whatever flow keeps everything the most silent, don't worry about anything else :mrgreen::mrgreen:

That is the whole point Mike.

Firstly we all have overflow commonly called prefilter boxes...Why call them this?

Because they are moving the surface water only from the tank when done properly, If you imagined that fish waste, coral waste and detritus was similar to oil it isn't hard to visualize oil floating on the surface of the DT, the prefilter box is there to remove it, the slower the removal the more concentrated that would be , if the extraction rate is increased the oil is mixed with more water and becomes diluted.
So this oil/ water mix then goes to the sump where some use filter sock for containing large bits etc, it then should enter the skimmer as concentrated as possible and then the skimmer can do it's job properly.

Why anyone would want to keep returning dirty water continuously back to the tank so they can keep skimming a little at a time is beyond me, get it out get rid of it and return clean water back to the tank.

I've always thought of it this way.. imagine that there is one car wash in the city and all the cars have to go through it. The car wash can only service cars at a certain rate, say 5 cars an hour? Unfortunately the cars can only wait at the car wash for so long before they have to move on (that is they can't sit there forever and wait), so cars are moving through the car wash at a certain rate independent of how fast the car wash can wash cars. As cars come in they get washed, or if they've waited for too long they move on and don't get washed. If cars come in very quickly, obviously fewer will get washed and will just end up passing on through unwashed and so the dirty car ends right back on the streets. If the cars come in slower at a rate that the car wash can handle then more cars will get washed. If it is a perfect day where the rate of cars coming in equals the rate of the cars being washed then all cars will get washed. Also, keep in mind that this is the only car wash in the city so all cars must eventually get washed, so eventually those dirty cars that had to pass through unwashed last time will eventually come back and try again to get washed. The faster they can turn around and get off the streets and come back to the car wash the better their chances of getting washed within a small time frame, but that also means they can't spend as much time at the car wash.

Agreed.

Slowly we can see the use of closed loops falling out of favour because of the high energy costs and a number of other reasons (tank wall integrity, OMs, maintenance, etc). That leaves powerheads and propeller pumps. Many people, a long time ago, decided they preferred to not have PHs in their tanks long term, if not for the appearance, then for safety. That leaves propeller pumps which are very costly once you get beyond, well, one. For this reason I think we will see large volume returns continue.

I don't use a pre-filter so I have nothing to add about that. I do use filter socks but that's just to reduce bubbles in the sump.

I'm gonna use the same car analogy. Going too slow means you are burning all the fuel that goes into the engine but you are not utilizing all the energy that the car is capable of, going too fast and you are not burning all the fuel that goes into the engine. In either case you need more fuel to get to where you want to go. The sweet number according to experts if I am not mistaken which they say would be fuel efficient would be between 60-80.
In a way if you have a tank that is 100 gal and you have a skimmer that has a pump rated at 800 gph and you have a turnover rate of 1 that would just mean that at least the same water goes through the skimmer 8 times. If you have a turnover rate of say 40 that would mean water would just be passing from your tank to your sump without even going to your skimmer. It you go around say 4-8 then the water would at least pass through your skimmer at least once or twice. I think that would be efficient enough. Going too slow and you are just going through water that has already been stripped of all those waste and oil and going too fast and you are not getting stripped at all.
Same thing with the heater if you have it in your sump. If it is too slow then the water is not heated up with evenly, if it is too fast then the water just passes through it without getting heated up at all.
best way is to just match the capability of your equipment with the turnover rate of your tank to your sump otherwise you are either wasting energy either it is just being redundant or not doing the job at all. It is going to be a trial end error thing but you will get the feel for it as it goes along.

Except that the sump isn't a separate unit; the tank and sump are the same system. The turnover rate should be a non-issue. What is important is that the overflow box is large enough to handle the volume going through it. If your OF is 10' long and is able to extract the surface of the water and not just a lot of water, it is running efficiently. This means you could have 1000x turnover in your 20 gallon tank. The amount skimmed off the surface, whether 10% or 100%, removed by the skimmer is a non-issue because the skimmer can only handle what it's rated for.

I think the issue here is redundant recycling of clean water, not turn over.

This whole argument is theoretical.

Am I going off topic here? The poster was asking how fast the turnover rate is suggested. And so is the analogy I was putting in there. A car is not separate from it's engine either. It may not be separate from your system but it contains a lot of your equipment. It may or may not be that the skimmer might be efficient with a slower turnover or not, believe what you want until a thorough study comes out about it. The skimmer isn't the only equipment in your sump some of them do need some lingering time to work efficiently at the same time they won't work well if the water was almost not moving.

The opening post asked about sump turnover,not tank turnover. whether you like it or not if you have an overflow box you do have a prefilter box they are technically doing the same thing, why are people saying as I said years ago that having no teeth in the oveflow box is more effective? why because it skims better.

There might be an ideal turnover rate if the skimmers were 100% efficient but doubt they're close. Even if they were, what's the big deal if one decides to have the return pump contribute to the overall turnover of the tank. Really, if one could accurately measure waste remove by our little hobby skimmers, would there be a significant difference between 1x, 2x, 5x flow through?