Question on flow versus turnover

[19frank90]

I've been doing some reading on the difference between flow (being the flow within the aquarium) and turnover (being the flow from the aquarium to the sump and back).

Flow: I have two MP40s which each run between 2100-2500 gph throughout the day (4200-5000 total). Ecotech's website lists the following recommended flows:

• 1869 gph - LPS recommended
• 3115 gph - SPS recommended
• ~4500-6500 gph - Optimal Zone

In a mostly Softie/LPS (w/ one monti), is my 4200-4500 overkill? Zoas, cloves and leather look great. Duncan is open but not extending as much (though I wonder if that has to do with switching to the Corallab AB+ SPS light settings from their LPS/softie setting).

Turnover: What I read also stated to optimize skimming, you should set your return pump at the flow your skimmer is rated. My Reef Octopus 152s is rated at 140 gph. By my understanding then, my return pump (2,000 gph max) should be set at only 1-2%, which seems wildly low. Thoughts?

 

[nereefpat]

What is the tank size?

The logic that a return needs to match the skimmer flow, in my opinion, is flawed. The skimmer isn't that efficient, and not all water flowing through the sump goes through the skimmer anyway. A good turnover rate through the sump is somewhere around 5x tank volume per hour.

 

[19frank90]

88 gallon display with a 24 gallon sump.

 

[nereefpat]

I would shoot for 300-600 gph through the sump. More is fine, as long as your overflow can handle it, and as long as it is reasonably quiet.

For the display, somewhere around 3000 gph is a good starting point, but you'll have to dink with it.

 

[19frank90]

I would shoot for 300-600 gph through the sump. More is fine, as long as your overflow can handle it, and as long as it is reasonably quiet.

For the display, somewhere around 3000 gph is a good starting point, but you'll have to dink with it.

I’ll tinker with those settings. Thanks.

 

[RocketEngineer]

The logic that a return needs to match the skimmer flow, in my opinion, is flawed. The skimmer isn't that efficient, and not all water flowing through the sump goes through the skimmer anyway.

Agreed. Having studied the science, I’ve never found anything that supports this myth. A skimmer is a multi pass filter. It can’t remove everything in a single go because it has to have a certain amount of material to form the foam head initially. Instead I recommend you have enough turnover to ensure the water chemistry in the sump matches the tank. On a big system, this could be as low as 2X the display per hour. The 3X-5X commonly quoted seems to be a good balance but needs to account for plumbing losses too.