Skimming 101

[mojoreef]

Well thinking about it we might be able to use the rule in reverse?? I think it would be safe to say that the water being taken out is being replaced by air correct??

Mike

 

[RedEyeReef]

Well thinking about it we might be able to use the rule in reverse?? I think it would be safe to say that the water being taken out is being replaced by air correct??

Mike

I would agree but then how do you acount for less water passing (replaced by air) through the skimmer, or is it irelivant?

 

[Scooterman]

Hey redeye, I had the TF 100 multi and converted to the sump model later, it is fed separately. Mike I think blocking off the air line increases the performance of the needle wheel as in acting more like a pump also I think once air is blocked it can build up more pressure to push large volume of water, just like a closed loop cavitating right?

 

[mojoreef]

I would agree but then how do you acount for less water passing (replaced by air) through the skimmer, or is it irelivant?

yea its a tough call. in the case of these venture skimmers they replace the water with air because of the reasoning Scott proposed, where as a skimmer with a seperate air supply adds to the existing water.

Scott what did you come up with your test??


Mike

 

[Scooterman]

I need to do this again & write down the information but before I can actually do a proper test I need to make some modifications, I'm waiting for aquarium liquidators to send me some more parts, he wants me to try a softer 3/8" air tube with a better flow control on it. He will also send a 3/8" fitting that I will drill and tap a hole in the cup side. I will run the new tubing to this fitting, thus sucking air from within the cup, he said this should quieten the loud noise I'm getting, I can't run the tubing wide open right now because the noise of air sucking in is so loud it is unbearable. Until I can set it up to suck in as much air as it is designed, I think the skimmer will actually perform better, then I can try and run test to get proper levels. At this time I have a smaller O.D. tubing inserted into the 3/8" tubing, I robbed some fittings from the hang on TF multi 1000 and ran the other end of the smaller tubing into a canister that makes everything very quiet, I even drilled out every fitting as large as I could. With this I ran some test, pinched off the air line and adjusted the water level to 20% of the neck height, the neck being 6.5" tall. I then released the air line and the water level dropped almost all the way down the neck. so at this point I removed the restricting tube to let the air rush in wide open, bubbles were much better, I again ran the same test with the same effects just more though, yes the water level dropped more when I opened the air line wide open. This is all of the testing I've done so far, I will attempt to try what the supplier wants until I can afford to convert the thing into an air stone skimmer, I really don't think I will ever get the performance otherwise, not even with restrictions on the air intake.

 

[NaH2O]

Alright - I fear I'm going to sound like a complete moron here, but I attempted to figure out the 20% thing. The calculations I came up with either show my skimmer really isn't as efficient as I once thought, or that it isn't so bad.

This is a needle wheel skimmer. Air and water come into the unit at the same place, near the bottom.

I'll post the dimensions of my skimmer, and the crude calculation of cfm, and maybe someone else can see what they come up with. My other half brought home some type of metering device to measure the air getting sucked into the tube, which he says isn't an ideal tool, but did the best I could. What he wanted to use and had access to use was far too large for this project.

I came up with a water volume of 4.5 gallons in my skimmer. I used the diameter of my skimmer (8") and height (20"), also added in some of the neck volume, as I keep my water level almost to the bottom of the cup (4" diameter neck and 4" height). Those are the numbers I used for gallons. If you want to disagree that's fine...I have so many scribbles on this paper, I'm lucky I can read anything.

The pump is a Sedra 5000, which is ~500 gph

The cfm's crude calculations came out to be approx 0.8 - 1.0 cfm. Does this seem right?

 

[Scooterman]

The pump is a Sedra 5000, which is ~500 gph

I don't really understand this part because how can this pump produce 500 gph, I'm thinking gph stands for gallons per hour right, gallons as in a fluid such as water, So if you lessen the pumps ability by removing the impeller & installing a needle wheel, that there reduces the pumps water moving performance, then you inject air so that also reduces performance. I'm using basically the same design, size but a claimed 900gph pump with the needle wheel, maybe I should down grade pump? I don't understand how you got the .8 cfm's or 1.0 cfm's from all that Nikki, how did you do the math? LOL, I guess if your sounding like the moron then I must be the moron LOL, & I like math ehhhh!

 

[NaH2O]

Scooterman - there is a forumla (included the area of the air tube) used to determine the cfm from whatever the reading was on the anemometer. It read the air going into the tube. BUT, its not like the measurement was done in a "controlled" environment, which is why I gave an approx value.

As far as the pump - I'm not sure what the "true" gph is....I found that spec somewhere online....I didn't even think about the impeller vs. needle wheel and how it would effect things. Perhaps, I should try and figure out the actual gph....I just don't want to take the skimmer out of the sump.

 

[mojoreef]

LOL Scott makes some good points. With these neddle wheels its tough to figure out exactly whats going on. Lets try to simplify this.

Nikki has a skimmer that holds 4.5 gallons of water. By appling the math 20% of that water mass should be air or about .6 cubic feet worth. I am not sure if this is an easy task for this kind of skimmer. If she is feeding the skimmer at approximately 500 gph its going to take about 30 seconds to fill it. So at a rate of 1 cf per minute that would mean that she is injecting .5 cfm of air everytime she fills up the skimmer. so pretty good on the on the air to water mix?
So one principle down. The next and really the most important concept is the bombardment rate. Or the ammount of time the raw water spends in the mixing chamber where the protien molecules are bombarding the air bubbles. In Nikki's case the water is spending 30 seconds in the chamber at best before leaving it. This does not leave much time for protiens and organics to attach specialy when one thinks it can take up to a 3 to 4 minutes for protiens to attach. so not si good thier for sure.
Now to add to that problem the air is being injected in the same location at the water, So each water goblet is going to be subjected to even less clean air bubbles becuae they travel the same path. Now if they were traveling apposing each other or counter current they would get a heck of alot more hits, even using the same figures, so not the best their either.

So appling the basic principles of skimming we could say tha nikkis skimmer has a good air to water ratio. Because of the fast moving water in the skimmer her bombardment rate and dwell time (contact time) are brutal. So when she runs the skimmer she is only taking out a small portion of the protiens and organics that she could, if she reduced the flow through rate and thus increased the dweel time and bombarment rate.

ok now I need to go to sleep.


Mike

 

[Anthony Calfo]

cheers, all

I am just "waking up" and catching up from dreadful jetlag (rarely hits me, but got me good this time coming back from Singapore).

I apologize for not chiming in (yet) to the thread, but wanted to say thanks and kudos to all for the tremendous input. A fabulous thread thanks to our paternal benefactor (Mike/mojo) seeding good threads/wisdoms as always.

I'm off to the other side of the world again next Tuesday and will likely be quiet here on RF still as I catch up this week with work, etc.

Looking forward to jumping back in a few weeks.

best regards,

Anthony

Ooh... and will see some of y'all at IMAC, no doubt

 

[NaH2O]

Going back to the basic principles of skimming, and like Mike posted, I have a good air to water ratio. There is nothing I can do about where the air and water come into the skimmer, but again, as Mike posted I can slow the flow. I can probably put a Sedra 3500 on the skimmer to allow for the lower flow and subsequent increased dwell time. Would changing the pump to something smaller effect the air water ratio? My initial thought is it wouldn't but I wanted to ask anyway. Also, since the air to water ratio is good, then adding an airstone to this type of skimmer wouldn't do anything for me, right? When the earlier skimming conversation started about Mike's airstone skimmer project, I remember wondering if the addition of an airstone would be beneficial....now I don't know if it would help, as it wouldn't do anything with dwell time.

 

[mojoreef]

Oh yea alot of help you are!!! lol

Ok lets do a quick concept over view.

1: flow rate through the skimmer. The formula for figureing it out is Hours=9.2 purity coefficient (which means that 99.9% of the water has been treated (gallons/gph) so this formula gives you an idea on how to see how many times a day the tank water runs through the skimmer in order to treat all the tank water completely. So an example of say my skimmer would be:I have a pump pushing 600 gph and my tank has about 1000 gallons of water and I want to have a treatment of 9.2 coefficient (which means 99.99% of the water is treated in the tank). Or (1000/600)9.2=15.3 So all my water will hae seen the skimmer every 15.3 hours. This formula works for all equipment.

2. Bombardment rate: Which is the number of times an assending air bubble hits a descending water drop with in the skimmer. This concept deals with the time the tank water spends in the skimmer and the diameter of the skimmer. Ok the formula for figuring this out is Bombardment rate (R) = the dwell time of the water/the dwell time of the air. So an example: my skimmer holds 30 gallons of water and is feed by that 600 gph so that means that the water completely passes through the skimmer every 180 seconds So my dwell time for the water is 180sec. The dwell time is a long formula and it just dont work for me, so I mickey moused it. I turned the air pump super low so thier was only a few bubbles in the skimmer. With the bubbles coming in and hitting the wwater flow in the skimmer I timed it out at a very approximate but it came out to 12 seconds, so my bombardment rate is 180/12= 15 bombardment rate. 10 is concidered to be perfect. So I should sow down the rate a bit.

The way a skimmer pulls off organics is really done in two seperate functions. One is mechanically and the other is chemically. With the bubbles hitting the water goblets it is mechanically pounding off the organics or seperating them from the water molecules. The chemical reaction is where the organic molecule is attracted to the surface of the air bubble. Now that chemical reaction does take time to occur, thus dwell time is very important.

Mike

 

[mojoreef]

There is nothing I can do about where the air and water come into the skimmer,

well you could, lol

I can probably put a Sedra 3500 on the skimmer to allow for the lower flow and subsequent increased dwell time.

no you cant do that because on your type of skimmer the water and air totals are tied to each other, its a venturi thing.

Also, since the air to water ratio is good, then adding an airstone to this type of skimmer wouldn't do anything for me, right?

thats right it wont help.
Nikki your skimmer is just lacking in the dwell times of both air and water. and the fact that it is less effective to add the air and water from the same point. What you could do is make your exisisting pump recirc the water and air and not have it deliver water to the skimmer. Then you could add a small pump to deliver the water to the skimmer and inject it from the top of the water column of the skimmer.

Now in saying that you have a brand new skimmer that is working decent, so I would be hesitant to butcher it unless you feel it is not working good enough.


Mike

 

[Scooterman]

I'm going to micky mouse my brain on this one a while LOL, good information.

 

[spongebob lover]

ok just to let you guys know you are making my head spin with all this math and bubbles, but i'm trying to follow :|

 

[mojoreef]

Its actually simple stuff, it just has some pretty complex math behind it. Their are all sorts of claims made by skimmer manufactures, pitting one type against another. Some of them have valid points others no so valid. With all the different schemes and types of skimmers out their its tough to know which way to go, and now days skimmers seem to have skyrocketed in price, so the call you make can be a very expensive one.
Bringing everyone back to the concepts behind skimming and the laws and principles the govern it, give folks a chance to to have everything on an even basis and then look at each type of skimmer and make your call.
With the laws and rules of protein skimming, it does not matter if the air is chopped, force driven, venturied, injected or magnetized. the rules are the same.

Mike

 

[Scooterman]

Mike As soon as I get a break, I think I'm going to do some butchering on a new skimmer lol, I think the re-circulation idea is an easy option, I think that is one reason the little tubbofloater was smoking my new super duper skimmer LOL, I will convert it to the same way as the TB 1000. It is either that or get an air pump & stone & right now I'm all tapped out. I really do like the Re-circ idea, I'll make plans and post pick of how I'll plan on doing it and if we succeed I'll even post success pics, at this point I don't think I have anything to loose, in Nikki's case well I think she has an excellent skimmer, costly for me so I went with a copy that isn't as optimized as hers. I will plumb the needle wheel like you said, sorta like the TB 1000, making it a 900gph needle wheel re-circ & then I'll feed water into the skimmer with a 1/2" line from a valve off my main return, this way I can control the flow rate into the skimmer. Then if it works I can drill a hole and hard plump the return water later if it works well, cool idea Mike!

 

[NaH2O]

Now in saying that you have a brand new skimmer that is working decent, so I would be hesitant to butcher it unless you feel it is not working good enough.

I feel the skimmer is working great, however, I really don't have another skimmer to compare to for this tank. I also can't imagine punching some holes and modifying my favorite tank toy . Well, maybe after the warranty period .

So maybe my question now is - how do you know you are getting the most of your skimmer, once its set-up? Can skimmate be the judge?

Euro-reef came out with a recirc design (shortly after I purchsed, of course), so I wonder if this makes up for what is lost with the design of my skimmer.

It would be nice if the manufacturers included these calculations with their product information. When shopping for a skimmer, I imagine it would be difficult to figure out these calculations without doing the measurements. I don't know if a call to the technical support department would give the answers about dwell time, bombardments, and air to water ratios.....prior to the purchase of a skimmer. Its hard to know what is talked up advertising hype with expensive equipment and 'name brands', or what is genuinely a good skimmer (at least that is what I'm learning from the thread). Even an understanding of the basics makes it difficult to know which skimmer would provide the best skimming for a given system. I suppose some hobbyists don't want to get the most out of a skimmer (fear of overskimming?), depending on the inhabitants....but I personally want to skim the best I can.

 

[Scooterman]

I don't know for sure but I'll go out on a limb that lots of it is marketing bs, raving mostly on convenience designs & quality of materials, the rest has been designed years long long ago, in boomer days I'm guessing

 

[mojoreef]

It would be nice if the manufacturers included these calculations with their product information.

good luck

Can skimmate be the judge?

Not really alot of folks will say the darkest skimate is best but how do you quantify that??? You could easily have more organics in a clearer skimate.

I suppose some hobbyists don't want to get the most out of a skimmer (fear of overskimming?),

Maybe that opens a whole other can of worms??? Supposed the high pressured, high flow skimmers force up to much planktonic life??? Hmmm would that make skimate dark?? lol anyway thats for another day.

Its hard to know what is talked up advertising hype with expensive equipment and 'name brands', or what is genuinely a good skimmer

Thier sure are and alot of these units are very well built with a great level of quality. Anyway that the concept of this thread, follow the rules and laws and the choice should be easy.

Mike