Another look at skimmer dwell time.

[basement reefer]

Those of you that have been reefing for any amount of time probably follow some sort of rule of thumb with regards to the amount of turnover your return pump needs to have.

Reasonable modern advice states that a good rule of thumb would be to match the GPH of the return pump with the GPH of the skimmer. The reason being this will give maximum dwell time in the skimmer compartment to keep the detritus from "short circuiting" the skimmer. They say we no longer need high turnover in the sump because we have wavemakers etc. that do the heavy lifting circulation wise.

Lets take a moment to think about this.






















If you have a machine (skimmer) that removes detritus from the water, wouldn't it stand to reason that said machine would be more efficient if you supplied it with the dirtiest water possible?

If a skimmer occupies a sump of skimmed-out water, how is that of benefit to lowering nitrate and phosphate in the display? We should disregard the future and consider the past. It's not about the pristine water you supply via return, it's the detritus we failed to capture in the past.

The return water is instantly diluted with dirty water anyway. The skimmer should be more effective if it occupies the dirtiest water possible. *All things being equal, maybe some skimmers can't handle regular water, though I doubt that for the most part. Actual dwell time within the skimmer and airflow are dependent on the skimmer model. All of them should appreciate being fed dirty water for the fastest development of skimmate.

A quick thought experiment. Lets continue to reduce the return flow. At some point the skimmer will no longer be effective from a practical point of view, sure the return water is clean but there is not enough of it to be meaningful. Beyond that point the skimmer is for all intents and purposes isolated from the display as you continue to cut off return flow.

Now lets go the other way, increase the rate of flow throw the sump. This will bring the amount of detritus in the skimmer compartment to saturated display tank levels. At this point the skimmer will have the maximum amount of detritus available at all times for export.

You probably don't need a lot of flow to achieve this. I suppose in theory you could compare the nitrate/phosphate levels in the skimmer compartment with the display to see if you have equilibrium.

I don't really have the duplicate equipment to do this as an experiment, but encourage others to do so.

 

[basement reefer]

Further thoughts. Matching the GPH of the skimmer and return is a good starting point IMO, I'm not disputing that. I'm just trying to get a tangible grasp of the interaction of the skimmer and the water in the skimmer compartment.

Our systems are quite different with regards to how the water flows through the skimmer compartment. For example in my sump, the entrance and weir are on the same wall, in other sumps they are usually opposite. If it weren't for the skimmer churning water within the compartment, the water would have little reason not to head directly to the weir. To further complicate things, my sump is a eShopps that splits the flow diverting it to the skimmer compartment and refugium separately. So even if I did match the GPH of the pumps, the amount that actually goes through my skimmer compartment is less.

Maybe this doesn't even matter much in the sense that it is easy to get enough flow, however as you can see in my case it can make you wonder. I have a monster skimmer for the size of my system so it wouldn't surprise me if my skimmer compartment was cleaner then the display.

I think one thing I have surmised from this is that I would like the skimmer to eject downstream from the intake. I would prefer it to not recycle water within the skimmer compartment.

 

[Saveafish]

I'll stick my neck out like a lonely chicken.. years ago the stands use to come 36" and 42" tall. Now over the years they are shorter. Making the skimmers has to be shorter as well. Heigth is the key. Higher they are the stronger the bubble attracts the protein. Google the 3 main proteins. Plant, fish and meet. Short fat skimmers don't have the raise amount to pull out other proteins. ETSS skimmers was TALL they can pull out ammonia and nitrates. Why because of heigth. They could pull out anything.
Its the lost heigth that kills a skimmer. If a skimmer is 20' foot in diameter but 6 inches tall. It wont pull much out. If its 10 foot tall and 6 inches in diameter, it will pull it all out.

 

[basement reefer]

Aspect ratio, that is a interesting point.
I had considered trying my skimmer on a stand based off of something I heard in a BRS live stream. I wonder if this is the same mechanism at work in the sense that it increases the pressure on the bubbles or is it shear dwell time in the tall chamber?