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Thread: Skimming 101

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    Skimming 101

    I thought I would start this thread Anthony to talk a little about the concept of skimming. Now days with so many different skimmer types and methods of generating foam and with the different claims to fame, from magnetically charged bubbles to recircualting and so on. I thought we could spend a little time talking about the basic concepts behind skimming.
    Feel like Playing around, anyone ??


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    Mike I have a few questions, one I saw where you recommended someone supplementing a skimmer with Ozone. I know this may be a little off subject but it was regarded supplementing a skimmer, is it practical to use OZ these days with skimmers, cost wise & safety wise?

    Ok now with that out the way, second part, I recently purchased a larger needle wheel skimmer, very large, I find it doesn't seem to produce as much nasty thick stuff as my little skimmer, I know it is only a month old but I'd think by now I'd have it tweaked out, which It will make wet skimmate at times, then for no obvious reason it flood like crazy, it looks like clear water, now this is the only common observation I've noticed between the new & old skimmers, they both at times would wack out suddenly and pour water over the top, any ideas as to why? After each term they would slow down again and seem to be ok. How do I know I'm skimming enough, is there a rule of thumb here, because I'd sure like to think I should be getting more now than before, maybe I should of just stayed with the small TB 1000? My apologies if I'm off subject, I think you're headed in another direction.

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    Scott on the use of ozone with a skimmer, for sure it is absolutely a great plan to use as a suppliement in the skimmer. Ozone is a organic eating machine and to be honest it does a better job then any skimmer could. If set up and used properly its a great add.

    On the skimmers, the reason I have started this thread as thier is a lot of info out thier but it seems to be in the form of the manufactures concepts or reasoning behind thier design. Most of the actual concept of skimming and the concepts behind it has been lost to hype of one brand or another. For me I have a really hard time trying to apply the laws governing skimmer to the different concepts, to be honest i dont know if I should wave my hands in excitement or laugh at the BS anymore. I thought if we dove into the principles a bit we could apply them to different designs

    On you skimmer, its hard to diagnose from here. If your skimmate is to clear and is flooding my first thought would be that the mix is incorrect and when their is a bloom or something simular in the tank (that would cause extra skimming) it floods. If you are not getting enough foam or bubble production then I would say lower the water level so when it does start foaming it doesnt over flow. Personally I have not had any luck with the needle wheel type skimmers. I find that the bubble production (although electrically efficient) really suck at putting out bubbles.


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    Thanks for the Ozone information, I think I'll back track to some of your threads on this subject.

    Now as far as my needle wheels, I'm frustrated I did lower the level, it seems to be making thicker junk but I have a bad feeling about this knock off design (no names) that everyone craves, Mike the bubbles are awesome as far as size, nice micro bubbles but here is the same problem I'm facing with both needle wheel skimmers, the amount of bubbles is horrible, trying several needle wheel pumps isn't the answer, If I could double the amount I know it would actually skim as it should, I wonder if I could convert it into an air-stone skimmer. 30 years ago when I first used air stones and I know what they are capable of producing with those little hobby air pumps, I can imagine what would happen if I purchased a real air pump & stone. Whatever, I'm totally unhappy with the bubble count, I know there has to be a better way.


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    I have a reletively large (24"x4") old venturi driven counter-current skimmer I plan on converting to an airstone driven one. As a venturi skimmer, it is less than impressive, but with the heigth of the skimmer, combined with the counter-current flow design, I think it will be much more productive with an airstone instead...

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    Well, since this is Skimming 101 and not 201...perhaps first discussing what a skimmer is supposed to do will help with the discussion on different types of skimmers. I know there was another conversation about skimming concepts, but I got lost on some of the points.

    Let me see if I have an initial understanding of what is happening. First - we are trying to remove organics. I understand there are different types of organics present in the water (dissolved, particulate, volitile) and we also remove things like bacteria, elements, planktons, uneaten foods...I'm sure there are more. There is a protein molecule in the water - one part of the molecule is attracted to air, while the other is attracted to water. The part that likes air (non polar) will stick to the bubble, while the part that likes water (polar side) points away from the bubble. So, I picture a ball (the air bubble) with fibers (bipolar molecules) sticking over the entire surface. The more air bubbles present, the more organics can be removed. But, also taking into account a greater surface area means more organics to be removed....that means more bubbles, but of a smaller size, then the more area for proteins to adhere to. Let me know if I'm off on any parts. One part of the equation for skimming is smaller bubble size with a lot of bubbles.
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    This will be very interesting for me. My skimmers are driven by needle wheel/impeller pumps. Not really sure what the proper term is. I'm assuming "needle" is referring to the type of impeller the pump has. My understanding is these are good skimmers because they chop the bubbles into smaller sizes. What are the other types and the pros and cons of each? I hope thats not to general of a question.
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    Scott I do agree the bubble size the neddle wheel skimmers is perfect and I also agree its the total amount that just kills it. From the research I have done on the subject and the experences with many different types their are a few Principles we should try to follow when looking at any type.

    One is the bubbles size, the smaller the bubble the more they pack and the more protien it can hold (sandbed theory).

    Another is the amount of bubbles. You want to see about 20% of your total water volume in air bubbles. Simple test is to turn off the air and make a measure as to the height of the water column in the skimmer, then turn the air on and you should see the water column rise 20% of the total height.

    A big one is the amount of protien hits the air bubble get. I am not sure how to do the math on the various skimmer types, but here is an example. If the water enters the skimmer at the top of the water column in the skimmer and exits via the bottom and the air bubbles are injected just above the bottom then all the water must pass through the air mass in order to exit. To me this seems to be the best way to achieve the hit ratio. But thier might be a good arguement about the needle wheel chopping up the water and air mix, I guess the same could apply to injector style units.

    Lastly is how much violence is thier in the skimmer, the more violence the more broken bubbles and thus the less protiens captured.


    So try to stick with in these guidlines and you should be able to tell how good your skimmer is mechanically.


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    NIkki you are dead on. now we have to take the mechanics into account as if thier is not enough foam (as in the foam never reaches the cup) adhesion doesnt really matter.

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    Quote Originally Posted by mojoreef

    A big one is the amount of protein hits the air bubble get.
    So lets look at how this is done. Is this water that is dumped into your sump at this point carrying a large majority of nasties from the main tank? I know the water is getting skimmed somewhat from above but like my tank for instance it isn't coast to coast so that effect is horrible, I think lots of nasties never makes it to the sump, only the finer decomposing nasties maybe? How can I make sure I'm getting the most out the main tank, will this improvement make the skimming effect overall better or no I'm wrong we don't need to worry about this because the nasties will get to the skimmer as long as we do have good upper flow in the main tank of coarse? Can we break this down a little more before we even bring it into the skimmer? Example. Ok, On smaller typical needlewheel skimmer lets say...this is where water falls off & into the overflow & into the sump, then gets sucked into the skimmer pump, at the end of the venture the air line is attached and sucks in air, the water/air gets chopped up at this point. I have a good percentage ratio of micro bubbles (somehow) would having my skimmer inlet in the main tank be a better option?

    I like that testing method, I've done it but never thought about a percentage of water to bubbles ratio will try that today.

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    On your point Scooty, I have noticed that when I use a surface overflow to feed the skimmer, I get more skimmate production than if the skimmer is fed from water below the surface of the tank. I think a lot of the gunk a skimmer can remove ends up on the surface (hence the oily sheen you see from time to time on the surface)....

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    I think lots of nasties never makes it to the sump, only the finer decomposing nasties maybe?
    Ok well that is starting to go into the realm of effective flow in the tank, but I do believe it does pertain. I would say it stands to reason that if larger particulate and simular dont make it to the skimmer because of ineffective flow or overflow eventualy the majority will at some point in their decomposition if maintence is done (ie blowing the rocks and the substraight).
    Ok, On smaller typical needlewheel skimmer lets say...this is where water falls off & into the overflow & into the sump, then gets sucked into the skimmer pump, at the end of the venture the air line is attached and sucks in air, the water/air gets chopped up at this point. I have a good percentage ratio of micro bubbles (somehow) would having my skimmer inlet in the main tank be a better option?
    Hits between air bubbles and protiens is defined by dwell times, not really a mixing functions. Does that make sence?? protien will attach to a bubble based on contact it doesnt need to be mixed, chopped, sliced or diced. So the longer the air bubbles are dwelling with the water the more protien hits will be available. So going to your question the more raw the water the better but I think if we start looking at the processes we can make a fiarly good idea as to if we need to increase the concentrations??


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    On your point Scooty, I have noticed that when I use a surface overflow to feed the skimmer
    Ok can you elaborate on how or exactly what you mean by a surface overflow feeding a skimmer? Sorry for the ignorance.

    Hits between air bubbles and proteins is defined by dwell times, not really a mixing functions. Does that make sense??
    Another great point I'm sure this is something to think about when making a skimmer, ie Taller tube or neck to allow for this right?

    So going to your question the more raw the water the better but I think if we start looking at the processes we can make a fairly good idea as to if we need to increase the concentrations??
    Great but I didn't want to jump in until a few questions for better understanding before getting into the processes, in another words I want to eliminate everything else up to the point where water hits the skimmer suction. So with that said, I can repeat myself here, first thing that sticks out is these super tall skimmers, not necessary big around but tall, I'm guessing this is one part that will ultimately determine the contact time because of the distance up the tube to the neck this micro bubble has to travel, thus allowing longer availability to be contacted by a waste particle, right? Ok guess that jumps the gun a bit, so maybe we should dissect the part where the water enters, the introduction of air, how it is mixed or processed by whatever means. I'm familiar with several including the air stone, & needle wheel but all the others there is some shady areas, so understanding each and their principals will be a big help. Once we (me or whomever lol) figure that out I think it will clear up some misconceptions but may also lead up wanting to actually see apple for apple which method will actually work better or should I say skim better maybe not efficient but pumps out the gunk better than any other way at whatever cost it takes, then go from there to maybe a more affordable but still effective skimmer. The reason I say this is so far I've seen only a few that to my inexperienced eyes looks very impressive & I'm not talking design, features or looks but the actual product it produces & the rate it can do it.

    I wonder if a combination of a needle wheel & air stone would be any better, is there limits of too less or too much micro bubbles?

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    I wonder if a combination of a needle wheel & air stone would be any better, is there limits of too less or too much micro bubbles?
    I don't know if there would be limits to too many micro bubbles, unless there was too much violence and the bubbles were crashing. Would bubbles from an airstone reach an area of too much violence (where the bubbles coming out of the needle wheel enter the skimmer) and break? When I look at the bubbles coming into my skimmer, that area seems pretty violent. I don't know if that would have an effect or not? Perhaps, they would simply go with the flow.

    How do you determine what size skimmer you need for a tank? This question seems pretty basic, but I do wonder where companies get their ratings from? I purchased the largest skimmer that would fit under my stand. 8" diameter, 30" tall....rated for 175 gallons (Euro-reef). Yet, a similarly made ASM skimmer...shorter in height (24"), 8 1/2" diameter tube, same exact pump, but is rated for 350 gallons. I don't get this? Sorry if this is going off in a tangent.
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    Another great point I'm sure this is something to think about when making a skimmer, ie Taller tube or neck to allow for this right?
    No not really Scott, you could have a skimmer that was say co current (water and air being injected in the same location) ad make it six feet tall and it would be the same as one 3 feet tall that was counter current (i am using rough numbers here) this is because the clean air bubble is not subjected to as many protien moles as it is traveling at roughly the same speed and the same direction.
    I'm guessing this is one part that will ultimately determine the contact time because of the distance up the tube to the neck this micro bubble has to travel, thus allowing longer availability to be contacted by a waste particle, right?
    not really, as I mentioned above their are many other factors and manipulations that can be done. Example: imagine virtually still water with bubbles rising throught it, What do you think the contact time would be??? (thats another clue, lol)
    the introduction of air, how it is mixed or processed by whatever means
    Hmm air and water dont mix....sorry I could resist.
    I'm familiar with several including the air stone, & needle wheel but all the others there is some shady areas, so understanding each and their principals will be a big help
    AHHHHHhhh Haaaaa that is why I started this thread. Not to answer that question as much to say when looking at protien skimming and choosing a skimmer we need to concentrate on the principles of protien skimming and NOT the manufactures suggested methods???? Once the concepts and/or rules are none then that part is easy


    Nikki
    I don't know if there would be limits to too many micro bubbles, unless there was too much violence and the bubbles were crashing
    yes thier is and the number is about 20% of the volume of water of the correct sized bubble
    Would bubbles from an airstone reach an area of too much violence (where the bubbles coming out of the needle wheel enter the skimmer) and break?
    to much air can cause a ton of violence, alot more then I would have imagined. A big thing with the combo air stone/needle wheel is that the venturi will only handle so much until it craps out the pump.
    How do you determine what size skimmer you need for a tank? This question seems pretty basic
    thier is a formula for that, we will play in a bit.


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