Skimmer Ratings- a discussion.

[Jeremy R.]

So then, understanding it is not a difinitve number and just a ball park..... what ever number you come up with..... how do you rate?

Say you say a skimmer is rated AT 90g tank. Is that at full capacity, with 10% head room, 20%? Not trying to ask you to pin point, I asking what factor do you feel is a good fit for a given tank? 1 times, 1.1, 1.25, 1.5 times?

Good question. Everyones tanks and maintenance habits are different. This is why I always ask the customer a series of questions that pertain to his or her system and future plans. When I come up with a range of DT sizes they are as direct and close as I feel comfortable getting without knowing further info about the customer and their tank and their expectations.

 

[Powerman]

Cool. I understand this is not a science formula that we plug in numbers and get an aswer. I assume we could discuss contact time, turbulance, air to water ratio, neck size, body diameter all day long. And at the end we would still arive at some ball park figure that has been learned though trial and error and experience seeing what "works" and what doesn't.

People want numbers, but I understand experience from a trusted source is a valuable thing.

 

[Powerman]

So then... we have a lot of needle wheel skimmers out these days. Some original, some copies..... Say the bodies, necks, pumps, and what not are all in a pretty common range.... just to even things up a bit.

I understand air draw is not the end all be all, but given that most other things are generally equal, is there a "ball park" figure for air draw for a given volume of water? I've heard 500 lph/100g thrown around. Is there any use in that number, or is it about as accurate as "watts per gallon"? Is LPH/g completely useless without knowing water flow, or air to water flow ratio?

 

[rkaires]

I believe there are so many variables in in rating a skimmer. Body shape, neck size, air/ water flow etc are just some. Some manufactures grossly over rate their skimmers and some are conservative. I guess air/water flow could be used to give you a baseline but it would still be guessing so to speak. Experience with a particular skimmer I think is the best way to rate it. Better manufactures will put a lot of R&D into their products. I am in the same camp as Jeremy and mojo. There is no substitute for real world experience.

 

[luke33]

Yep, everything has been said pretty well imo in the thread. Generally when rating a cylinder skimmer i would use the 4-6-8lph rule. 4lph air draw for low, 6lph air draw for med, and 8lph air draw for high bioloads. Thats 4-6-8lph per gallon of tank. So a 100g tank would need 400-600-800lph air draw depending on how it was stocked. Now this doesn't mean diddly squat unless its a well designed skimmer. Meaning nice body with decent dwell time, correctly sized neck and good transition. The flow through has to be there as well. I don't think that dwell time is as important as everyone use to think. There was an old wise tale about a 2min dwell time. I have mimicked the 2min dwell time in many recirc tests and the only thing i can see different is i can pull darker skimmate out with a longer dwell time. I can pull more skimmate out with a faster flow through and less of a dwell time. Look at how crappy of a dwell time a large beckett skimmer has and how much skimmate production they create. Now with the new cone skimmers out there the 4-6-8lph per gallon rule has changed. I can't say what % increase a 600lph cone has over a 600lph cylinder but its a significant increase in capability. I have been testing a 70scfh askoll cylinder vs a 38scfh cone and the cone has shut down the askoll completely. Can a cone handle twice the load as a cylinder? No, but i think a properly designed cone can handle atleast 25% more than a properly matched cylinder.

 

[Powerman]

I agree. In my line of work, I can read all the tech manuals I want, but experience is the best teacher.

That is basically my problem, I have knowledge in this hobby, and I strive to understand, but I don't have hands on time. I have owned a EV-120, BK Mini 160, and a K2. I just played with a SWC Ex 200 for a month.

Just the same, skimmers seem to be an integral component for a successful reef, they have been in use for quite some time, yet there still seems to be a fundamental lack of knowledge on the subject in the hobby.

All it ever seems to come down to is that I bought this one cause some guy told me it was good. While the "old timers" that have been around a while are an invaluable source of info, the consumer is still at the mercy of "this company claims it's the best thing since sliced bread", and has no real way to judge the product for himself in terms of numerical data if he is new to the hobby. I suppose it's the same way in many hobbies, but you would think skimmers would be a little less clouded at this point.


To be fair... I suppose a major obstacle to some sort of standardization is the fact there is no such thing as a standard tank.

 

[ksed]

Yep, everything has been said pretty well imo in the thread. Generally when rating a cylinder skimmer i would use the 4-6-8lph rule. 4lph air draw for low, 6lph air draw for med, and 8lph air draw for high bioloads. Thats 4-6-8lph per gallon of tank. So a 100g tank would need 400-600-800lph air draw depending on how it was stocked. Now this doesn't mean diddly squat unless its a well designed skimmer. Meaning nice body with decent dwell time, correctly sized neck and good transition. The flow through has to be there as well. I don't think that dwell time is as important as everyone use to think. There was an old wise tale about a 2min dwell time. I have mimicked the 2min dwell time in many recirc tests and the only thing i can see different is i can pull darker skimmate out with a longer dwell time. I can pull more skimmate out with a faster flow through and less of a dwell time. Look at how crappy of a dwell time a large beckett skimmer has and how much skimmate production they create. Now with the new cone skimmers out there the 4-6-8lph per gallon rule has changed. I can't say what % increase a 600lph cone has over a 600lph cylinder but its a significant increase in capability. I have been testing a 70scfh askoll cylinder vs a 38scfh cone and the cone has shut down the askoll completely. Can a cone handle twice the load as a cylinder? No, but i think a properly designed cone can handle atleast 25% more than a properly matched cylinder.

Luke is it possible that the askoll skimmer is to large for the bio load in the aquarium so therefore it will loose the foam head quicker than the smaller cone?

 

[luke33]

Sure its possible to use to large of a skimmer and that will happen at times. But in my case i've been running the askoll skimmer for a year now and have never had it stop skimming. I have also ran numerous skimmers with it and never seen this. I have a pretty heavily stocked 125g with 50g sump. 70scfh is pushing it but its ok if your heavily stocked. I know quite a few people with smaller systems running larger skimmers then me.

 

[Jon Warner]

one of my favorite topics

I've personally designed a bunch of them...

And skimmer sizing is a really big deal.

Some manufacturers give realistic ratings... and some don't.

What goes into a rating? Just lph of air? Ahhh... no. It's all about volume of body, volume of neck and production of air. And then you take variables that affect efficiency and use them as a force multiplier. Cone body, +1... Well designed cone body +2... VBT Bubble Ring +2... Stepless Neck, +1... Well engineered bubble plate +1.

I'm a big believer in body volume. There is NO 6" diameter skimmer made that can skim a 250 gallon tank well... none. And with volume must come the air... air lifts particulate.

Larger body frequently wins given equal or greater air flow. Using a non-WM example, the SWC 300A skimmer will outperform an SWC 11" cone IME on a heavy bio-load.

And the precious NECK... oh the precious neck, the true heart of the skimmer. As the neck goes, so will go the performance of the skimmer. Too large a neck and you must run the water level too high in the body to skim, too small a neck and it's an overflow waiting to happen. That neck MUST be matched to the pump and to the body volume... note other skimmers out there that are "over-necked" from the factory and they compensate by putting too much pump on a specific body size creating mass turbulence and mediocre performance.

And that precious neck must ALSO be matched to the bio-load of the system.

That massive 6"+ SWC 300A neck will NEVER work right on a 90G tank, never. Because it "overskims"? NO! Don't use that phrase!! There's no such thing, but there IS such a thing as too much neck for your system. The volume of the neck is directly related to the system bio-load. Thus, MANY people who put skimmers with 5"+ necks on sub 150g systems will have problems.

Balance

Balance

Balance

The best skimmers are the ones that have balanced:

Body Volume
Neck Volume
Air Flow
Water Flow

For example... a fantastic skimmer for a 90G system would have a 6" diameter body, 3.5" neck, about 750-800LPH of air.

And it will OUTPERFORM that bad-*** cone with the 8" diameter base, 1800LPH of air and the 5.3" neck on THAT SYSTEM.

 

[Powerman]

Awesome Jon, thanks.

So then that brings up an interesting question. You can't "over skim" a system. The skimmer will only pull what's there, you you can have improperly matched skimmer size to tank size. So if I go the ever popular "2 times tank size" then what will happen to my tank? What is the bigger skimmer not doing that a properly sized skimmer is?

If you do not like oversizing a skimmer, then what factor do you feel you can get away with and still have a well performing skimmer. 1.5 times, 1.25 times?

If... and only IF.... you know you will be moving up in size, and you buy a bigger skimmer to go on the future bigger tank.... what do you feel is the max size difference a skimmer can span? 1.5 times...2 times...3 times. Meaning going from a 90g to a 180g or a 270g tank. At what point is the skimmer pretty useless on the smaller tank and useless on the bigger tank?

 

[mojo]

Well Said Jon, I know I have preached balance for some time. And I know in conversations we have had we have similar opinions as far as pumps and such as well.

Every company has there own ratings and some are driven by experience, some are driven by what the competition rates theirs at, and some just guess. All in all there is no set answer in my opnion. 1x 1.5x 2x ect.. it takes knowing what the pump can do, the body volume, neck size and air draw to know if that skimmer is going to work well or not.

You can give me the specs of a skimmer and anyone with enough skimmer experience could probably tell you if its going to work well or not and give a realistic tank rating.
Now I havent owned every skimmer on the market but I have owned about every popular skimmer on the market or have used one for a short time. And some brands I have used many models. Example. Warner marine I have used the k2 prototype 4.3 in neck the production model with 4.5 in neck, the s150, the s200, the as 150, and the as200.
The vertex in 100 gen 1 and 2 the vertex in 180
Euroreef
bubble king
ATB
Alpha's
SWC
MSX
Octo's
Bermuda's
AquaC
ETSS
MRC
ASM
Tunze
ect ect ect...
as the list goes on. I got to the point I started to build my own. I have gained a lot of respect for several people on here and other places as well as they may be more experienced in something than I am. But Vice versa. I may have used something the havent .

I agree with Jon again. Its all about the balance of the skimmer amd the needs of the hobbyist.

Mojo~

 

[ksed]

one of my favorite topics

I've personally designed a bunch of them...

And skimmer sizing is a really big deal.

Some manufacturers give realistic ratings... and some don't.

What goes into a rating? Just lph of air? Ahhh... no. It's all about volume of body, volume of neck and production of air. And then you take variables that affect efficiency and use them as a force multiplier. Cone body, +1... Well designed cone body +2... VBT Bubble Ring +2... Stepless Neck, +1... Well engineered bubble plate +1.

I'm a big believer in body volume. There is NO 6" diameter skimmer made that can skim a 250 gallon tank well... none. And with volume must come the air... air lifts particulate.

Larger body frequently wins given equal or greater air flow. Using a non-WM example, the SWC 300A skimmer will outperform an SWC 11" cone IME on a heavy bio-load.

And the precious NECK... oh the precious neck, the true heart of the skimmer. As the neck goes, so will go the performance of the skimmer. Too large a neck and you must run the water level too high in the body to skim, too small a neck and it's an overflow waiting to happen. That neck MUST be matched to the pump and to the body volume... note other skimmers out there that are "over-necked" from the factory and they compensate by putting too much pump on a specific body size creating mass turbulence and mediocre performance.

And that precious neck must ALSO be matched to the bio-load of the system.

That massive 6"+ SWC 300A neck will NEVER work right on a 90G tank, never. Because it "overskims"? NO! Don't use that phrase!! There's no such thing, but there IS such a thing as too much neck for your system. The volume of the neck is directly related to the system bio-load. Thus, MANY people who put skimmers with 5"+ necks on sub 150g systems will have problems.

Balance

Balance

Balance

The best skimmers are the ones that have balanced:

Body Volume
Neck Volume
Air Flow
Water Flow

For example... a fantastic skimmer for a 90G system would have a 6" diameter body, 3.5" neck, about 750-800LPH of air.

And it will OUTPERFORM that bad-*** cone with the 8" diameter base, 1800LPH of air and the 5.3" neck on THAT SYSTEM.

Hi Jon

That was very well said.
I was wondering if we could get another opinion from you. It is probably the second most talked about in the subject of skimmers, and that is where should the cone transition start from. We here it should be full cone, the cone should start from the bubble plate, or a cone like the Super Marin is enough. Where do we draw the line on the benefits of the cone shape.

Thanks

Kevin

 

[mojo]

I am sure Jon will chime in. In my opinion If I have a cone I like a full cone. As the as the water travels downward the cone gets larger allowing the water velocity to slow down as it exits the skimmer. If you can slow this down you can reduce the turbulence a small amount in the reaction chamber. There are a couple cones that do what a cone should do. The cone is suppose to reduce turbulence in the reaction chamber. And in theory the bubbles that pick up the organics in the water all rise upward. In a turbulent chamber the organic that collect on the air bubbles will collide with other air bubbles causing them to pop and causing the organics to fall and attach to another bubble. So a cone is suppose to be more efficient in bringing the dissolved organics to the collection cup. But again not all cones are created equal. When you watch the skimmer run you should see the bubbles rise off the bubble plate, not swirl back down below the plate. You should see the bubbles come to the side of the cone body and rise straight up. Not a bunch of swirling around. If you see this turbulent action then you are not getting the use of the cone body you should.
Now The k2 jon created does do this probably the best of any of the cones simmers out there. The ATB does a good job of this as well.
If you have a nice balance of pump, water , air and body you should see the "rise" off the bubble plate. Many skimmers use a skirt, a ring around the bubble plate to make sure the bubbles go upward and not sucked back into the exit pipe causing micro bubbles.

Now that doest mean cylinder skimmers dont work. lol. They use more brute force to get the job done. still work great. But in theory the cone should be efficient atgetting the same job done.
Sorry for rambling on as I havent slept much but I hope this makes sense to you all.
:beated:

 

[skimmy]

well, Jon nailed it, not much to add to that but,

just want to throw in my 2 cents here.... :tongue:

to me the whole question of which skimmer and why begins with tank size, BIOLOAD, and feeding requirements for individual creatures.

from there it's just a sort of rolls down hill as to the requirements of the skimmer.

so, the bioload, tank size and feeding would determine the size requirement of the main skimmer reaction chamber, the size of that reaction chamber would determine the size of the neck and the amount of air injection. from there the decision would be based upon type of air injection, type/quality of pump, build quality, budget, and "proven skimmer performance/longevity".
a short hand version of this is to usually consider primarily the air injection numbers... if your dealing with a reputable skimmer manufacturer that has done his homework, like WM, deltec, ATB, BK, SWC, then the neck size, and reaction chamber size will already be properly calculated for the air injection.

my typical preference for skimmers is cone shaped bodies, pinwheel impellers in low watt pumps that have bubble plates for turbulence, process more air than water(you DONT want a skimmer to process alot of water, and this is the main drawback to using a single pump for air injection and injecting process water) gate/knife valve outlets for minor adjustments, and for sps quality water, at least 600 lph air injection for every 100g high bioload.

 

[skimmy]

also, having installed, maintained and repaired skimmers for well over 10 years, I have an affinity for inexpensive skimmers that can "hang with the big boys"... as I know how fickle customers are to spend money on gear, and they only usually spend about half as much as I personally would(if I could)...

 

[Powerman]

my typical preference for skimmers is cone shaped bodies, pinwheel impellers in low watt pumps that have bubble plates for turbulence, process more air than water(you DONT want a skimmer to process alot of water, and this is the main drawback to using a single pump for air injection and injecting process water) gate/knife valve outlets for minor adjustments, and for sps quality water, at least 600 lph air injection for every 100g high bioload.

The only air/water ratios I have heard are from SWC and WM. That the best would be a 1:1 ratio, but that isn't possible. 1:2 air to water is about as good as it gets. I have not heard of a skimmer that moves more air than it does water.

600 lph of air for 100g of water is a common number, but at what turn over rate? How many GPH. Using a 1:2..... that would mean roughly 300 gph for a tank turnover rate of 3 times an hour.

 

[mojo]

bk gives water volume on there ratings too ...usually..

 

[luke33]

The sicce and askoll pumps are the closest to a 1:1 ratio air vs water. Sicce can do nearly 300gph air at 350gph water. (with pw)

The askoll can do 670gph air and 700-800gph water. (with pw)

 

[Powerman]

How are you measuring water?

 

[Powerman]

bk gives water volume on there ratings too ...usually..

Nice.. thanks. On most of their line, at least on Salty Supply, it is a 1:2 air water ratio. It would be great if more companies did.