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Perfeshunal Hikk
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Discussion Starter · #1 ·
This thread isn't intended to be a thread about particular skimmer brands. It is intended to be an information thread where information about skimmers and designs is put together in the hopes of coming up with some kind of document that people can be referred to when they ask about different elements about skimmers.

The information in this thread is not all my own. A lot of it is from me reading, researching, talk to people that have built skimmers, tinkering with pumps, etc. If there is something I post that someone has read somewhere else, its entirely possible that I may have read it there also.

If there is something in this thread that is inaccurate, please post a correction so that it stays as accurate as possible.

With that said, the first post is more of a "Hikk threw this together" type post to get something started and have something for people to ask about, comment on, expand on, and hopefully get the thread going.
 

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Perfeshunal Hikk
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Discussion Starter · #2 · (Edited)
The most efficient skimmer design is a counter current design where the water is moving in one direction (downwards) while the air bubbles move in the opposite direction (upwards). Typically they are built with airstones driven by air pumps with a feed pump pumping the water in the top and draining out the bottom. The biggest issue/complaint was with maintenance. Having to clean/replace the airstones.

So, people started hunting ways to get air bubbles into the skimmer without the airstones. Enter the venturi and becketts. There are two ways to get air into a water pump stream. Before the pump (venturi) and after the pump (beckett).

I use the terms venturi and beckett generically. Venturi refers to a device used to pull air in before the pump, and I use beckett to refer to an injector that pulls air in after the pump. The one exception would be if you were using an air pump to force air into the water flow.

The becketts draw the air in after the pump. They use a pressure rated pump (high electrical usage) to force water through the beckett injector which in turns draws air into the water flow. The issues with becketts are the pumps you need to run them with (high wattage) and still having to clean the injectors periodically.

The venturi pulls air in, the air goes through the pump and gets chopped up and then sent into the skimmer body. Mesh mods, needlewheels, pin wheels, are all designed to chop the bubbles up smaller. The efficiency with venturis are the big thing now with companies trying to get more and more air in without using more and more electricity to get the air in.

If you build a skimmer that is 6' tall, unless you have one horrendously large pump to move it in a circular motion, the water/bubbles at the top of the skimmer will be moving in a vertical fashion rather than in a circular motion around the body. Why waste the energy to get it in a circular motion if its going to be vertical in the end? Simply start with it moving vertically. Enter the bubble plate.

Bubbleplates are designed and used to cut down on the turbulence in a skimmer body and get the bubbles moving straight up in a semi-orderly fashion. The concept behind it is that if the bubbles are moving in an orderly fashion, then they aren't colliding with one another and keeping the skimmate from attaching to the bubbles to be removed from the skimmer.

The flip side is the "tangential injection" skimmer where the water is intentionally introduced at an angle(to horizontal) in an effort to "spin" it around the chamber as it goes upwards in the hopes of increasing contact time with the bubbles. Whether it actually does that or not is a big debate. As the water spins around the tube, it has to move faster to get to the same place at the same time as if it weren't spinning.

With skimmers being built shorter in order to fit into a stand, the dwell time suffers. You have a shorter body so you have less contact time with the air/water. Enter recirculating skimmers. If you take the water that is already in the skimmer and "recirculate" it back through the skimmer, you can increase the contact time and increase the potential to skim the water. It requires a second means of introducing water. Either gravity (drain fed) or a second pump to put water into the skimmer body. A recirc skimmer has to be designed with recirc in mind. Some single skimmer bodies do not recirc very well simply because of the design of the initial body.

Edit: I used the word "Venturi" to refer to pre-pump injection through out this thread when in fact a venturi goes after the pump and also requires a pressure rated pump to operate correctly. A Beckett and a Mazzei injector are both forms of Venturis and all have to go after the pump.
I am not sure what the air inlet mechanism on a "needlewheel" pump where the air is drawn in before the pump is actually called. If anybody knows, please let me know?
 

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uber-stupid
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I just thought it would be easier to deleat this post then to try to repair it. I will repost after my thumbs stop cramping.
 

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Perfeshunal Hikk
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Discussion Starter · #4 ·
Recirculating skimmers don't recirculate the air bubbles. They simply recirculate the water. The air is injected with each new pass of the water. Its tantamount to taking the drain from a skimmer and hooking it to the inlet of the pump. The pump itself actually gets a little better performance in a recirc situation because its in a closed loop situation. In a "standard" configuration, the pump has to overcome the head pressure from the water in the skimmer. With it in a recirc setup, the water is pushing on the inlet of the pump and helping the pump overcome the head pressure (same as a CLS pump does) and you get a little better performance from the pump as far as air being introduced to the skimmer water.

The drawback is that you have two more holes in the skimmer body and you either have to drain feed it from the tank or run a second pump.

Imagine you had a skimmer that was 6' tall and the pump circulated the water through it at 600gph. The air would have contact time with 6' of water. If you cut the skimmer down to 3' tall in order to get the same 6' of contact time, you would have to put the water through twice to get the same contact time.

The advantages to a recirc design are that you can control the input of water independent of the air introdcution. If you have a single pump, the water goes in at whatever rate the pump puts it in with the air. If you have a recirc pump, you can speed up/slow down the introduction of water without having to increase/decrease the introduction of air into the water.

I am not a very good technical write (I suck at it) so hopefully by the time I get to 20 posts or so in this thread there will be enough content that someone with better technical writing skills than I have can help me organize it better.
 

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Perfeshunal Hikk
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Discussion Starter · #5 ·
Tangential Injection.

Term that typically refers to putting water into the skimmer body at a tangent to the pipe. Simple english? At an angle to the body so that it attempts to send the water in a circular pattern around the body. The theory is that if you get the water to travel in a circular pattern to the top of the skimmer body, then it travels further so it increases contact time.

To me (and I could be wrong), if the water is travelling further then it has to travel faster in order to drain at the same rate. If its travelling faster, then you are losing the gained contact time. I am not absolutely sure that is true but it makes sense in my head.
 

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this may be a dumb question, but what would be an optimal contact time for the water? to me it seems that after x amount of time pretty much all of the waste you will get out of that water will have taken effect and it would be time for new water and to go through the system to pick up more waste. i realize that it would all depend on the skimmer and the bubble production, but in general what would the the best dwell time be around, roughly? if that makes any sense
 

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Perfeshunal Hikk
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Discussion Starter · #7 ·
Personally, I think if you ask 100 people in the hobby that question, you will get about 88 different answers. I don't think anybody knows for absolutely sure. I know Hop has told me that 2 minutes for some of the compound DOCs. Have absolutely no reason not to believe and a lot of reasons to believe it.

Part of the reason I don't think you can put a number on it is because parameters in the tank can make a difference. Salinity plays a part in skimmer performance. The lower the salinity, the harder it is for the bubbles to stay small without collapsing. You can see that, profoundly, by running a skimmer in FW and SW and see the difference in bubbles. So the contact time at, say 1.018 (FO) and 1.026 (Reef) is going to be different to get the same DOC out of the water. Simply because the bubble size is larger so it takes a lot more bubbles to get the same surface area and that means more contact time.

Also, the "dirtier" the water, the more bubbles it will take to clean it. If you set up a tank and test any skimmer on it with a set feed pattern, then you double the feed pattern, the skimmer settings will have to be changed. There is simply more in the water to try to get out so you need either more bubbles or more contact time to give the bubbles time to do the job.

I think that may cause more questions than answers though :(
 

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Perfeshunal Hikk
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Discussion Starter · #8 ·
One type of skimmer I have forgotten to mention so far, and may remember others as this goes on, is a downdraft skimmer. I have read a little about them but never seen one in person. The concept (from what I remember) is similar to a beckett style setup but uses bioballs (or similar media) in the "downdraft" tube. I will try to find my links on them again and see if I can get something summarized and posted along with links to the original articles.
 

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Carpe Noctem
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this may be a dumb question, but what would be an optimal contact time for the water? to me it seems that after x amount of time pretty much all of the waste you will get out of that water will have taken effect and it would be time for new water and to go through the system to pick up more waste. i realize that it would all depend on the skimmer and the bubble production, but in general what would the the best dwell time be around, roughly? if that makes any sense
Personally, I think if you ask 100 people in the hobby that question, you will get about 88 different answers. I don't think anybody knows for absolutely sure. I know Hop has told me that 2 minutes for some of the compound DOCs. Have absolutely no reason not to believe and a lot of reasons to believe it.

Part of the reason I don't think you can put a number on it is because parameters in the tank can make a difference. Salinity plays a part in skimmer performance. The lower the salinity, the harder it is for the bubbles to stay small without collapsing. You can see that, profoundly, by running a skimmer in FW and SW and see the difference in bubbles. So the contact time at, say 1.018 (FO) and 1.026 (Reef) is going to be different to get the same DOC out of the water. Simply because the bubble size is larger so it takes a lot more bubbles to get the same surface area and that means more contact time.

Also, the "dirtier" the water, the more bubbles it will take to clean it. If you set up a tank and test any skimmer on it with a set feed pattern, then you double the feed pattern, the skimmer settings will have to be changed. There is simply more in the water to try to get out so you need either more bubbles or more contact time to give the bubbles time to do the job.

I think that may cause more questions than answers though :(
I read an article about 3-4 years ago that focused around skimmers used for industrial waste use, cross referenced for our aquariums. The point of the article was to indicate that more complex DOC need upwards of two minutes of dwell for effective removal. What I've been looking into is does the removal of these more complex DOCs matter in aquarium usage since water changes alone may be of the greater benefit than these larger skimmers.

Case in point is the recent (last few years) implementation of shorter skimmers, more air and better waste removal. In fact I recently became one of these people... Certainly I don't have a peer reviewed article, but I can say that my taller skimmer with more dwell time and less air, produced 4 times the skimmate as this short skimmer with double the air???

I'm sure I'll have more thought later on this to organize in posts, but ultimately I'm just a hobbyist and not a scientist:D
 

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Perfeshunal Hikk
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Discussion Starter · #10 ·
Case in point is the recent (last few years) implementation of shorter skimmers, more air and better waste removal. In fact I recently became one of these people... Certainly I don't have a peer reviewed article, but I can say that my taller skimmer with more dwell time and less air, produced 4 times the skimmate as this short skimmer with double the air???
Personal experience is always better than some peer reviewed article anyway :)

I wonder how much of the difference is related to your old one being a recirc and the MSX250 not being a recirc skimmer?

I'm sure I'll have more thought later on this to organize in posts, but ultimately I'm just a hobbyist and not a scientist:D
If I waited until I had all my thoughts organized, I might not ever post anything. Post away, we can sort it all out later :)
 

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uber-stupid
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I think there is a definite limit on useful dwell time. Too long of a dwell time and the air will disolve into the water along with any docs it may have picked up.

As far as the vortek skimmers go. Even if the bubbles were traveling faster they would pick up more docs. Like dumping gas on a sidewalk... It will evaporate into the air eventually but the air will only have a certain saturation rate based on the density of the vapors the higher the density the lower the absorption. Meaning if you put a fan to it the vapor density will be drastically reduced and the absorption will be drastically increased.
 

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Perfeshunal Hikk
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Discussion Starter · #12 ·
I think there is a definite limit on useful dwell time. Too long of a dwell time and the air will disolve into the water along with any docs it may have picked up.
It would be interesting to see a test to compare how much air is put into the skimmer versus how much air actually leaves the skimmer. You couldn't test the water, it would have to test the volumes entering and leaving. Testing the water for oxygen content could, potentially, give adverse readings by virtue that one water test would be on "dirty" water (pre-skimmer) and the second test would be on "clean" water (post-skimmer). I don't think that any skimmer you could build in a hobby setting would ever run into an issue with dissolving oxygen to the point that it became detrimental to performance though.

As far as the vortek skimmers go. Even if the bubbles were traveling faster they would pick up more docs.
If the bubbles/water have to arrive at the same place at the same time, the contact time will be the same. Longer distance/faster travel versus shorter distance/slower travel. The contact time would be the same. I am not sure as to which is actually better though. It seems to be a big debate about skimmers as to whether the longer distance is a bigger benefit or not. And, how much of the turbulence caused by it causes problems. A lot of skimmers employ tangential injection and a lot use bubble plates and none of them are what could be called "bad" skimmers.

Although, personally, a lot of my beliefs in bubble plates is based on Bubble King skimmers in particular. Whether my beliefs are right or wrong, I don't know for absolutely sure. And not even sure how you could start setting up an experiment to directly compare the two different setups. The BK's are just so freaking incredible that it makes it hard to simply discount a bubble plate.

Like dumping gas on a sidewalk... It will evaporate into the air eventually but the air will only have a certain saturation rate based on the density of the vapors the higher the density the lower the absorption. Meaning if you put a fan to it the vapor density will be drastically reduced and the absorption will be drastically increased.
I don't think its the same though. If the water/air has to travel to the same point (the drain) in the same amount of time, and one has to travel further then it travels faster. But, it has to get there at the same time. And if it gets to the drain at the same rate, then the contact time *must* be the same.
 

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uber-stupid
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I have actually tried to watch an individual bubble to see what it does in there. It aint easy.
 

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im just starting to get into the technicalities of skimmers and do not have much working knowledge just yet. wouldnt a simple way to increase contact time while not having to build rediculously large skimmers be to just slow the water flow and use a secondary air pump to inject air. i realize that by just simply slowing the supply pump you would slow the air production as it is sucked in by the venturi, but if you injected air, would that not work?
 

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uber-stupid
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Slowing the suply pump means less water will be processed. True the water leaving the skimmer would be cleaner due to spending more time in the skimmer and possibly getting skimmed several times. But over all less water gets processed. The cleaner water is, the harder it is to get the docs out of it. so given the same amount of air and the same dwell time it is better to have a higher flow of water. I think.
 

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Perfeshunal Hikk
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Discussion Starter · #16 ·
im just starting to get into the technicalities of skimmers and do not have much working knowledge just yet. wouldnt a simple way to increase contact time while not having to build rediculously large skimmers be to just slow the water flow and use a secondary air pump to inject air. i realize that by just simply slowing the supply pump you would slow the air production as it is sucked in by the venturi, but if you injected air, would that not work?
Thats basically how a counter-current skimmer works. You have airstones in the bottom of the skimmer running off an air pump. The water gets pumped into the top and drains out the bottom. The water is going one direction, the air is going the other direction. The end result is that you increase contact time with the bubbles.

It is also part of the idea behind a recirculating skimmer. A recirc skimmer allows you to adjust the amount of water going into/out of the skimmer without affecting the air injection into the skimmer. If the water is coming out too "dirty", you can slow the feed pump down but you are still injecting the same amount of air so you increase contact time. If the water is coming out too clean or you think it can skim more water, you increase the feed rate which lowers contact time.

The main difference to me, fundamentally, between the counter-current and recircs is that the counter-current allows you to increase contact time with the same bubble. The recircs increase contact time but not with the same bubbles. Its basically increasing the size/capacity of your skimmer without increasing the physical size of the skimmer.
 

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Carpe Noctem
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Personal experience is always better than some peer reviewed article anyway :)

I wonder how much of the difference is related to your old one being a recirc and the MSX250 not being a recirc skimmer?
I'll recant this statement and say that after a few minor tweaks, my new, short skimmer is probably pulling out what the RC, 4' tall skimmer was. I'll have to report back in a month or so, but I would say that it is comparable now. but...

Custom RC skimmer:
$1400.00 plus $100 shipping
$139 for feed pump
Took 24"x24"X48" of space
Drawing about 200 watts
Loud... needed wetroom to run without modifications

In sump skimmer:
$500 shipped with extended collection cup
No feed pump needed
Takes up empty compartment of sump
Drawing about 52 watts

Can't hear it running

So far Each seems to pull about 1 gallon of skimmate every three to four days.
 

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Carpe Noctem
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I've stuck this thread for a while as I feel it has some benefit to many hobbyists;)
 

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uber-stupid
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How about a recirc that has a gravity feed from an over flow that feeds to the top for counter current.

Also, i was wondering if i put a gate valve on the input of the pump before the venturi (like skimmer>gatevalve>venturi>pump>skimmer) if I could close the gate valve slightly to increase vacuum in the line where the venturi is to increase air injection into the pump? There would obviously be slighlty less water but I think it would greatly increase the amount of bubbles.

Also can you do a mesh mod to an orca pump?

Im going to high jack this thread for my own personal gain, BWAHAHAHAHA!!!!!
 

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Perfeshunal Hikk
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Discussion Starter · #20 ·
Thanks Hop. Knowing that the shorter skimmer is, in essence, out performing the taller skimmer is interesting to say the least. A lot of what I post/think is from me thinking about it and nothing beats real world experience. I may have a new tinker room where I can throw some things together and see what does/doesn't work and see if I can learn some more about them. I am not sure why I got so interested in them but skimmers definitely have a certain appeal to me trying to figure out how/why they work and why some configurations work better than others.
 
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