Recirculating skimmers a gimmick????

[college429]

I don't understand the function in the design of recirculating skimmers.

The efficiency of skimming is primarily a function of chamber size, dwell time, amount and size of the bubbles, and turn over of the tank, the design of typical recirculating skimmers does not affect any of these.

The short path of the recirculation does not significantly affect dwell time.

Bob Goemans', Ph.D. book Protein Skimming & Activiated Carbon Secrets suggests too much turbulence (bubbles chopped again or colliding at high speed) can actually disloge from the bubbles what we are trying to extract.

Again, I can't understand what this tiny loop of a recirculation could possibly accomplish.

Is this just a gimmick?

 

[lvpd186]

I think there are some advantages to having a recirculating skimmer. For one there is less load on the recirculating pump so I think it will work more efficiently at pulling air. Also I think the design does affect the dwell time, but not in the way your thinking. The increase in dwell time does not come from the path through the recirc. pump, but rather from the design in the plumbing in the skimmer. Most of the recirc. skimmers I've seen have their plumbing set up where they take water out of the lower portion of the skimmer and inject it back in to the top portion of the skimmer. That in combination with the exit of the skimmer being at the very bottom of the skimmer gives the water going through the skimmer more time to get injected with air especially since there is a good chance of it going through the recirc. pump more then once. As for the other issues of the skimmers that you brought up; the NW recirc. pumps produce very small bubbles and the chamber size of recirc. skimmers is usually bigger then standard skimmers (but I'll let someone else, who has more experience with them, go in to those points). So, IMO, I don't really think it is a gimmick at all.

 

[ridetheducati]

As long as the recirc pump is pulling bubble free water, overall skimmer performance goes up. A poorly designed recirc skimmer pulling the same fine bubbles is counter-productive and does not benefit from increased dwell time.

Some say a recirc model adds 20% performance. How did they come up with that number? I wish I knew.

 

[college429]

Very good information/thoughts.

Based on what the premise that you are recirculating water from the bottom with few bubbles, wouldn't it be the same as putting more water through the skimmer from the aquarium?

Meaning wouldn't running a 500 gph pump on a non-recirculating skimmer vs. running a 400 gph pump plus a 100 gph recirculating pump be the same effect?

I also would like to see some substantiated numbers on the increase in performance.

 

[UCanDoIt]

I'm no scientist, but when I switched to a good recirculating skimmer, I saw more than twice the performance compared to other major non-recirculating companies and this was when I was feeding with a powerhead from the sump. But when my plumbing was redone and I gravity fed directly from my overflows, that's when the performance was impressive. My local dealer has tested same model recir and non-recir side by side and his subjective opinion is that there's at least a 15%-20% difference in performance.

What I like most about a good recirc model is that it gives the user total control over your skimmer in terms of deciding how fast to past water through your skimmer plus type of foaming and skimmate.

 

[lvpd186]

Some say a recirc model adds 20% performance. How did they come up with that number? I wish I knew.

I know what you mean. This hobby is terrible for unsupported claims by manufactures. It really makes it hard to gage how well something will work without asking other people (like here on RC) first.

Meaning wouldn't running a 500 gph pump on a non-recirculating skimmer vs. running a 400 gph pump plus a 100 gph recirculating pump be the same effect?

I understand where you are coming from but I don't think it would be the same. On a standard skimmer if you "push" 500 gph in to it then you are going to have 500 gph coming out of it. The water gets that one pass through the skimmer. The idea of a recirc. skimmer is to keep the water in the skimmer longer. Most recirc. skimmer manufacturers recommend a feed pump or rate at 1 to 1.5 the total tank volume. So on a 100 gal tank you would only push 100 to 150 gph through the skimmer. Thats a lot slower feed rate then a normal skimmer (you don't need a big pump to feed the skimmer since the feed pump doesn't create the bubbles like on a normal skimmer), but at the same time that water is being "recirculated" through the skimmer more then the single pass in a standard skimmer. I hope that makes sense. :rollface:

 

[Fishbulb2]

I think Ucandoit brought a great point. You get a lot more control. You can decrease the flow rate through the skimmer entirely independently of air draw and water height within the reaction chamber. You can't do any of those things with riser tube non-recirc skimmers. If you decrease the air flow, the water through the skimmer will greatly increase. Most of the time, non-recirc skimmers are just plug and play and can't be optimized very much. Next, I think the ability to plumb a recirc skimmer directly to your overflow makes a huge difference in my experience. I used to have a tiny Turboflotor 1000 (which is a recirc) and it used to pull out way more stuff than my current riser tube style non-recirc. I will never get a non-recirc skimmer again unless I plan to modify it. My experience has definetly been positive with recircs. It will be interesting when I modify my current skimmer to be set up this way because then I can compare the same skimmer, on the same tank with just two different configurations.
FB

 

[college429]

Anthony Calfo seems to be as skepticle as I am.
See his comments here: http://forum.marinedepot.com/Topic25344-13-1.aspx

 

[college429]

Here is another good argument against recirculating skimmers in the following article: http://www.cs.cmu.edu/~cap/raid/skimmers/thoughts/
Quotes:
"The best plumbing arrangement, from the point of view of maximizing efficiency (both measures), would be to pump water directly from the aquarium through the skimmer. After a single pass through the skimmer, the water would drain back to the aquarium..."
"Maximize flow between the aquarium and the skimmer"

 

[UCanDoIt]

I would stick to what you believe and buy and setup based on your beliefs. Like I mentioned when my local dealer did a side by side test of 2 exact same models, but one was recirc and the other not, it was a SUBJECTIVE OPINION that the recirc pulled out more gunk than the non-recirc of the same model, approximately 15%-20% better. So, I'm not here to argue the point, I just love the 2 recirc skimmers I have on my tanks and wouldn't want to change anything.

 

[RandyStacyE]

I always thought that the purpose of recirc skimmers is to get the most performance out of the pump and more air in the skimmer.

With recirc skimmers the pump does not have to work anywhere near as hard as it does when the pump is 'driving the skimmer'.

The pump doesn't have to push water 'through the skimmer' or battle head pressure within the skimmer therefore more air can be brought into the reaction chamber. That is the soul purpose of the recirc pump ... to put air into the skimmer without having to push water 'through'.

The amount of water that actually goes through the skimmer is adjustable. How the skimmer is fed water is versatile (from overflow or pump).

 

[Fishbulb2]

<a href=showthread.php?s=&postid=8887130#post8887130 target=_blank>Originally posted</a> by college429
Anthony Calfo seems to be as skepticle as I am.
See his comments here: http://forum.marinedepot.com/Topic25344-13-1.aspx

Well I read this thread and I didn't really agree with Anthony. I thought Steve's correction was much better. There is no reason at all why a recirc design should need a second pump and add heat and wattage. I think a big benefit of the recirc design is taking the most nutrient laden water directly from the overflow before it get's diluted back into the sump.

 

[sjm817]

The recirc skimmers have some nice convenience features.

Can be run external
Unaffected by sump water level
Can turn the air tap off to empty cup instead of turning skimmer off
More control over air and water throughput.

 

[college429]

Thanks for your thoughts.

I understand there is a lot of anecdotal evidense that it is more efficient.

It still seems to defy logic because the recirculation serves to keep the water in the chamber longer by drawing water without bubbles from the bottom, but actually what is more important is to keep the individual bubbles in the water column longer. That is why taller skimmers work better.

Actually it would seem recirculation should be less efficient, because as the water resides in the chamber longer, it gets cleaner, and skimming "dirtier" water is more efficent.

Just my thoughts.

 

[prance1520]

Taller skimmers are only more efficient to a point (the point of nutriant saturation), then your just running a "full" bubble up through more water.

I think the two main points of recircs are:

1. More emphasis on pulling air, less on pulling water. If you check out the meshwheel ideas, people are pulling hundreds of LPH of air while making smaller bubbles, this means the water has a better chance of hitting a small, "unfull" bubble to attach its nutriants too.

2. The ability to skim pure overflow water is priceless. If anyone should agree with this point, its calfo. If your using a calfo like overflow, you've got the highest concintration possible of nutriants going into the skimmer.

So this leaves you with the most nutriant-laden possible water meeting the most amount of and smallest currently possible bubbles. This says to me this gives you the highest chance of removing the nutriants.

But this is just my way of thinking.

Matt

 

[nyvp]

where is spazz when you need him

 

[Bob Goemans]

High quality skimmers properly sized to the existing bio-load are not in the need of having their reaction chamber water re-circulated! Would less quality units' benefit or those improperly sized to the bioload? Possibly, - as their dwell time, bubble size and skimmer width/height may be inadequate. Nevertheless, the length of time for bubble-bombardment is then extended in these 'less' quality units, and to what degree this affects their (bubble) surface area/charge capability is not something quantifiable in my opinion. So guesswork will have to do, and there's one other factor to consider, - is someone making a profit from recommending and selling them!
Bob Goemans

 

[UCanDoIt]

<a href=showthread.php?s=&postid=8928366#post8928366 target=_blank>Originally posted</a> by Bob Goemans
..... is someone making a profit from recommending and selling them!
Bob Goemans

of course, someone is making a profit selling them, that's why you have:
EuroReef (rating 135g)
RS135 $329 - CS-RC135 $668

H&S (rating 225g)
150 $599 - A150 $649

But in observing my local dealer test the same model side by side on the same tank, with the non-recirculating skimmer in sump and the recirculating skimmer also in the same sump, but gravity fed from the tank's overflow with the excess flow going directly to the sump, I saw a subjective 20% better performance with the recirculating skimmer.

 

[Fishbulb2]

Certainly a huge group of people have done this experiment in a fairly controlled manner. Basically the ASM recirc mod crowd. It's the best control for comparing the exact same skimmer, same tank, same bioload, only with a different configuration. From what I remember, these people reported better results in the recirc mod. My own feeling on it is that the increased dwell time is what allows them to remove more protein. Some DOCs take minutes to fuse to a bubble. Most recirc skimmer recommend only about 1-1.5X flowrate through their skimmers which leaves the water in the reaction chamber for a lot longer. Most non recirc skimmers have a much faster flow rate through them and thus probably not enough time for some organics to fuse to the bubbles.
FB

 

[Fishbulb2]

<a href=showthread.php?s=&postid=8928517#post8928517 target=_blank>Originally posted</a> by UCanDoIt
of course, someone is making a profit selling them, that's why you have:
EuroReef (rating 135g)
RS135 $329 - CS-RC135 $668

Oh and yes, this mark up is absurd!

FB