Skimmers in Series

[ReefsandGeeks]

Has anyone considered or tried running two skimmers in series to increase the organic recovery potential? The reason I ask, if the company I work for has a new water purification system (420,000gallons per day DI water capable) that uses two skimmer like devices in series. With the two skimmers in series, they are able to change the settings between the first and second skimmer so that the second skimmer is able to get more organics out of the water than the first one could. They change the air/water inlet rates and something else but it was able to get more out than say a skimmer that's just double the size. They could run them parrellel, which could have more thru-put, but not as clean as in series.

There are quite a few other processes involved in the water system, and is several 53' tractor trailors in size. Wish I could post pics of it, as it was amazing and I had an hour long 1 on 1 tour with the lead designer. It's all confidential stuff though, so sorry to say, you'll all just have to imagine it.

This had me wondering if there'd be any value in buying two smaller skimmers instead of one skimmer that's rated for twice your systems volume. I've heard that skimmers realy only remove 30-40% DOC as they are now, but in series may get 50-60%? just speculating on that. I don't recall where I read about the 30-40%. I dont have a spare skimmer to test, but it would be interesting to see the result if someone were to test this. Fiddle around with the second skimmers' settings to remove even more organics.

 

[Tang Salad]

Is the system you described a single-pass system, or does the same water continually recirculate?

If it's single-pass, then that could explain why 2 skimmers work better than one. Aquariums recirculate, they're not single-pass, and that is why people IME don't ever use two skimmers together. When they do, they usually find that one skimmer does all the protein removing while the other does nothing.

There's an explanation of this here. It's a little difficult to follow, but it's still the best explanation I've come across.

 

[joshbrookkate]

Would it make difference if one is in the sump and one is HOB?

Would it make difference if one is in the sump and one is HOB?

See below. Double post, sorry.

 

[joshbrookkate]

What about if one is in sump and one is HOB?

What about if one is in sump and one is HOB?

I ask because I have a very small footprint for a skimmer in my sump but I recently replaced my Reef Octopus HOB 2000 with an Eshopps S100 for my 75g tank. The RO did a much better job skimming, IMO. So I was thinking of using both skimmers, one in-sump and one HOB. Then I saw this thread. I read the attached article and it suggests if using 2 skimmers, to put them as far apart as possible, and I can do that. But I don't want to waste hydro on something that is not going to improve performance.
Any thoughts?

 

[Tang Salad]

There's no harm in trying, and I'd be very curious to hear the results if you do, but my guess is you'll find that one skimmer ends up doing all the work and the other won't remove anything at all.

 

[ReefsandGeeks]

The system I looked at was single pass. I get the artical I think, but the articleseemed to imply identical settings on both skimmers. I was thinking same skimmers, but a greater air intake into the second skimmer, which would have it's input directly from the first skimmer's outlet. With the same settings, I agree that the second skimmer would likely do very little. But I was thinking that the additional air would help get that little extra, without overflowing because the first skimmer would have already removed most of the organics. I'd test it myself if I had a spare skimmer. Not about to buy one as mine is keeping up just fine.

Josh, if you already have the 2 skimmers, I don't se any harm in running both. If one perfermes poorly, than it's very easy to just take it offline.

 

[RocketEngineer]

devastator007,

Look at it from a different perspective.

The water leaving the skimmer has a reduced DOC concentration compared to the rest of the water in the system. This "clean" water then gets mixed into the system and therefore the overall system DOC concentration is reduced. Now, this slightly reduced water is fed back into the inlet side of the skimmer where it removes more of the DOC. Repeat hundreds of times an hour.

You don't need a second skimmer to do this. The vast majority of us actually have a recirculating setup because the skimmer discharge is in the same water volume as the skimmer inlet. No need for fancy as the KISS option works just fine.

 

[2_zoa]

Escobal referenced 2 skimmers in series. One skimmers outlet was the other skimmers feed. So there was no mixing of the first skimmers effluent before it entered the second skimmer. This was counter current air stone skimmers. I also seem to recall a TOTM on here a while back that ran a DIY air stone skimmer setup like that. IIRC he also used oak for the diffusers. Anyway, I believe Escobal referenced this style setup to compensate for a lack of height or diameter as the recommended height was 4' tall.


Edit: now today's skimmer. One could probably do this with a recirculating skimmer. Since they require a seperate feed.

 

[Tang Salad]

the articleseemed to imply identical settings on both skimmers.

Yeah, I think what it meant there was that if you wanted both skimmers to be productive, then they would need to be exactly identical. But because of slight manufacturing differences, and different placement in the aquarium, they would never be exactly matched and so one would always out compete the other and the other would essentially be doing nothing.

I think RocketEngineer gave a great explanation. In a closed system like a reef tank, water is continually recirculated and so a single skimmer is essentially run in series with itself, reskimming its own output ad infinitum.

 

[coralsnaked]

Yeah well I don't drink the same KoolAide. If you have 3X the flow thru your sump as the skimmer intake pulls water in. IE a 1500 gph return feeding a 40 gal sump w/ a skimmer utilizing a 900 gph pump which is pulling in air and water reducing the water inlet to ~60% or 540 gph then you have ~ 1000 gph that never enters the skimmer in that hour of closed loop. Now add another identical skimmer sitting side by side not in series and together they pull 1000 gph of looped water instead of 500 gph. Now only 500 gph passes in each looped hour without passing thru the skimmer. In reality together they will pull more organics out than a single skimmer. Not 2X the amount but significantly more. That is of course considering that there must be a saturation of organics in excess of both skimmers potential. If a single skimmer can pull organics down to a negligible amount then an additional skimmer would have no noticeable improvement but then neither would a single bigger skimmer either.

 

[Tang Salad]

Yeah well I don't drink the same KoolAide.

Huh. I didn't see much Kool-aid drinking here. It looked more like a regular discussion.

Anyway, in your scenario, water is passing through the sump faster than a single skimmer can process it. Where does that unprocessed water go? Back to the tank and then back to the overflow, getting skimmed again by the same skimmer. Adding a second skimmer would only decrease the amount of time it takes that unprocessed water to get processed. And it would only decrease it by the amount of time it takes the system to complete a turnover of the entire system volume. Since most systems turnover, at a minimum 3-5 times an hour, you're looking at most at a 20 minute advantage by including the second skimmer.

In other words, you could add a second skimmer. Or you could wait 20 minutes to get the same effect with only one skimmer.

 

[2_zoa]

Huh. I didn't see much Kool-aid drinking here. It looked more like a regular discussion.

Anyway, in your scenario, water is passing through the sump faster than a single skimmer can process it. Where does that unprocessed water go? Back to the tank and then back to the overflow, getting skimmed again by the same skimmer. Adding a second skimmer would only decrease the amount of time it takes that unprocessed water to get processed. And it would only decrease it by the amount of time it takes the system to complete a turnover of the entire system volume. Since most systems turnover, at a minimum 3-5 times an hour, you're looking at most at a 20 minute advantage by including the second skimmer.

In other words, you could add a second skimmer. Or you could wait 20 minutes to get the same effect with only one skimmer.

I agree. IMO. If the skimmer was sized proper, the skimmer will "catch up" to the tanks production. As mentioned, bubbles can only remove so much junk from the water column. Advanced aquarist did a great experiment (twice) putting skimmers up against each other.
Again, I think the whole reason for the 2 skimmers linked together is to increase dwell time. Something most modern skimmers struggle with. Adding two independent skimmers will NOT increase dwell.

 

[PhaneSoul]

what if one were to tune one skimmer to skim dry and the other to skim wet?

 

[Tang Salad]

what if one were to tune one skimmer to skim dry and the other to skim wet?

My guess (again guess) is the wet one would skim as usual, and the dry one would skim little or nothing. It could be interesting to try though. Better yet, add different styles of skimmer, like centrifugal, injection, venturi etc. It is true that dry vs wet skimming takes out different stuff, as does centrifugal afaik, so if all were working together you could in theory fine tune what gets skimmed out.

 

[d-man]

I tun 2 smaller skimmers that equal out to my water volume. My first skimmer is right next to the drain lines. It then skims that water and thee it water then runs out directly in front of the pump for my other skimmer. They are both in the same compartment however.
The skim on the first skimmer is usually a lil wetter and still nice and dark. The skim on the second skimmer isn't as much usually but is always dark and there is tons of gunk that build up on the skimmer neck near the top.
When I take one off line to clean it for a few days, the skimmate on the other one still doesn't increase in volume usually. So, yes I do believe this does help a bit with two in line, sized appropriately.

If we never added anything to our systems then yes, one skimmer would essentially be able to remove it all at some point.but we continually add supplements, food and our hands. All this adds up. It's like having a conveyer belt with 1 person checking for QC or 2 in line. The second person will get what the 1st person cannot/misses, etc

 

[reefgeezer]

Two skimmers skimming high DOC water would be more efficient than one of them skimming reduced DOC water. I would suggest that you run the two skimmers individually.

Try adding citrus infused vodka to lemon-lime Koolaid to help it go down easier. :lol2:

 

[Tang Salad]

It's like having a conveyer belt with 1 person checking for QC or 2 in line. The second person will get what the 1st person cannot/misses, etc

I'm not disputing your results, but your analogy isn't quite accurate. A better one is that you have a conveyor belt that goes around and around in circles. If there's only 1 person doing QC and they miss something, that something will come around again in a few minutes, so that 1 person will probably get it the 2nd or 3rd time around. That's assuming they aren't overworked or undersized to begin with.

So if that's accurate, then the question becomes one of time. Namely, is the amount of extra time it takes 1 person to QC significant enough to cause a problem?

 

[ReefsandGeeks]

what if one were to tune one skimmer to skim dry and the other to skim wet?

This is where I was trying to get at, but said better. I get that our aquaruims recirculate, so anything missed will come back around in time. What I was thinking is if the first skimmer is able to remove a max of say 40% of the total organics from the water, no matter how many times it cycled through than maybe a second skimmer with different settings ie "wet skimming" would be able to get more of the organics out which the first skimmer wouldn't be able to get out because it's set to get the bulk of the organics out, but not tuned to clean tank water as finely as the second. I have no idea if that would work like that, or if the second skimmer would not remove any additional organics. Kind of different oganics.

 

[2_zoa]

Maybe the "second" skimmer should also be rated smaller so it can produce with less DOC in the water?

 

[ca1ore]

Too lazy to search, but skimmer comparison studies have pretty consistently stated that a skimmer is effective at removing about 30% of the organics. The only thing that would seem debatable is whether quicker removal of that 30% offers any benefit. There are countless posts here saying how running a significantly oversized skimmer results in overall poorer performance. Whether true of not, it suggests that the benefit of skimmers run in series, or in parallel, are suspect.