flow rate through sump

[jacksonpt]

I've been searching/reading trying to decide on a return pump for my tank. I've read more than once about how you don't want too much flow through the sump because it will reduce the efficiency/effectiveness of the skimmer.

Why?

Seems to me that as long as the skimmer is pulling in "dirty" water and spitting out "clean" water, who care how fast the water around it is turning over.

What am I missing?

[Timmy77]

Not sure but when I reduced my flow I noticed much darker skimmate and clearer water.

[Luckylouse]

I have a flow of 1700 glh flowing through my sump on a 90 gal system and 40 gal sump. Mu Bubble king 180 needs to be empties every other day.

[BLKTANG]

30x turnover rate in my sump.

[am3gross]

the reason for the slow turn over rate is so the skimmer has more time to interact with the water. if you run 500 gph thru it it will work better then if you run 1800 gph thru it... i have my skimmer set upi where it is fed from one of my overflows, so it is getting roughly 600 gph thru it. my total system volumn is around 240 gallons so the 600 i have going thru it is a little on the slow side.. but it makes for better skimming so i am happy!

[Playa-1]

I've been searching/reading trying to decide on a return pump for my tank. I've read more than once about how you don't want too much flow through the sump because it will reduce the efficiency/effectiveness of the skimmer.

Why?

Seems to me that as long as the skimmer is pulling in "dirty" water and spitting out "clean" water, who care how fast the water around it is turning over.

What am I missing?

It's not all about the skimmer. It depends on many factors and the skimmer size and rating is one of them. I will throw a few of them out there off the top of my head. It becomes inefficient when you send more water into the sump then the skimmer or filtration system is able to process effectively. At that point your just moving water around and you can do that much more efficiently with power-heads in the DT or possibly a closed loop system. Another issue is that high volume sumps have more potential to create nuisance micro bubbles, splashing, salt-creep and drain noise which are also virtually eliminated with the use of power-heads and closed loops. Larger pumps usually mean more heat, more noise, larger plumbing, more money and higher operating costs.

[ReefTECK]

Well certainly what has been said so far is supportive of the idea that slower water flow through the sump is beneficial, and some other good points about micro bubbles and operating costs.

To answer your question more directly, the reason a skimmer is more efficient at low flow rates through the sump is because the skimmer then has access to recirculate the water again and again. Skimmers aren't 100% efficient at capturing organic waste on the first time through.

Second, is that most skimmate is made up of particles that would otherwise become detritus, if you are passing these through without giving them the opprotunity to slow down and thus give the skimmer multiple attempts to remove them, they will most probably end up shooting back into the display tank and settling out in the corners and crevices of your display tank. Now this will happen anyways with some detritus undoubtebly, but if it makes it into your sump before settling else where, let your skimmer have some time with it.

After all, pushing more water about isn't going to do that much more for you anyways in the way of increasing dissolved oxygen and such, well you may not want it to, water can become super saturated with oxygen after all.

This is an intuitive answer based on my understanding of the fluid dynamics involved in this situation. So it might not be perfect but hopefully it will provide some working insight.