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Thread: Air powered filter flow rate

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    DIYFK member WickedSticky's Avatar


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    Air powered filter flow rate

    Since air pumps only state how much air they pump. Does anyone know what the nominal flow rate would be of a box or sponge filter would be, relative to the air flow rate? And I realize, using an air stone, tubing length, lift tube length and diameter are all factors, but just in optimal conditions roughly how much water would an air pump that pump 10gph of connected to an empty box filter move?

    Im making a filter for a 10gallon tank, I have an 19gph air pump (1200cc/min) and a 50gph submersible pond pump, trying to figure out which one is more powerful, google is not helpful

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    DIYFK member Meep's Avatar


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    No way to really estimate the flow rate based on air rate as there are many other variables involved, at best you might be able to toss out some random estimate but I suspect that will likely be nowhere near correct, especially over time as the filter clogs that will slow the slow 'suction' rate exponentially over a more constant water pump rate.

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    DIYFK member WickedSticky's Avatar


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    i realize there are lots of factors, clogging isnt one of them, two identical filter connected to a powerhead vs an air pump both clog at the same rate if the flow is the same. An estimate within 50%-200% is fine and probably as close as anyone can get. It would be a PIA to test but thats the next step if no one here knows

    A tetra air pump rated for a 40 gallon tank moves 20 gph air, a tetra power filter rated for 40 gallons move 210 gph water.

    So my 19gph air pump will be moving 19gph, or closer to 200gph either way its a big difference to the 50gph powerhead

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    DIYFK member Meep's Avatar


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    Click here to enlarge Originally Posted by WickedSticky Click here to enlarge
    both clog at the same rate if the flow is the same.
    But, pressure and suction rates are not the same...

    Consider the difference between a 2.2 GPM kitchen sink faucet and a 2.2 GPM high-pressure water sprayer, same flow rate drastically different abilities.

    I'm not sure where you are going with the numbers, air pump rating per aquarium gallons is just marketing, nothing more... I don't even use air pumps in most of my fish tanks as it's a waste since the filter pump is already agitating the surface enough to oxygenate the water.

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    DIYFK member WickedSticky's Avatar


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    wouldnt the both work by suction?

    Anyway I could have worded my question better. Dumbed down version: Im making an internal filter, with a submerged lift tube output. Would i get better filtration if I used an air pump that moves 20gph air, or a water pump that moves 50gph water.

    My assumption (probably a wrong one) the rating for a filter is hype, each company claims something different but the same company (tetra) uses the same criteria for all their filters to determine filter capacity. (for example, Tetra decides that a filter for upto 40 gallons means the minimum flow rate to handle the bioload of 12 guppies)

    So if Tetra's:
    40gal internal filter moves 170gph water.
    40gal power filter moves 210gph water.

    Logic dictates that the Tetras 40 gallon airpump moves should move around 150-240 gph water under optimal condition*

    A 50gph powerhead seems more powerful than a 20gph air pump. But based on my non-scientific tetra criteria research its not

    *Click here to enlargeptimal condition being the box filter has the ideal diameter and length lift tube, bubble size, bubble quantity, head pressure, tubing length etc... the maximum possible water flow

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    DIYFK member Nil13's Avatar


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    There are airlift flow calculators out there, but I'll tell you right now, you're not going to get 50 gph water from a 20 gph air pump regardless of what other design factors there are in the airlift. Iirc, the ideal air:fluid ratio wrt airlifts is 1:1. So that would be 20gph water ideally. But don't quote me on that, you're never going to get "ideal".
    ETA: even with 100% submergence and ideal conditions, you are unlikely to do better than 1.0 air flow :0.75 water flow in an airlift.

    Airlifts can't deal with head pressure so they will clog faster than a powerhead filter.

    Airlifts can be fantastic. They can move water very efficiently. However if energy efficiency isn't a concern, powerheads are pretty simple to use. I am a fan of airlifts. I think the simple sponge filter is pretty underrated and if you look at what the koi guys in Belgium are doing with airlifts due to outrageously expensive electricity, you'll probably be surprised at the volumes of water they are moving. Airlifts are pretty easy to power with batteries or an oxygen tank in a power outage because of the aforementioned efficiency. They don't have any moving parts to wear out. They don't chop stuff up into little bits. They have quite a bit going for them.

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    DIYFK member Meep's Avatar


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    Click here to enlarge Originally Posted by WickedSticky Click here to enlarge
    Logic dictates that the Tetras 40 gallon airpump moves should move around 150-240 gph water under optimal condition*
    I'm still not figuring out where you are going with this, as I said the Tetra 40 rating of an air pump is nothing but marketing nonsense, it literally means nothing... Regardless of the box saying it's rated for a 40 gallon tank or not that is simply gobbly goop to get people to buy it nothing more... The same '40' air pump would work perfectly fine in a 500 gallon tank, as it's primary purpose is to just agitate the surface, and the surface area is far bigger variable than the gallons of water...

    The Tetra 40 puts out about 1.3 liters/min or about 20.6 gallons of air an hour, no way that small volume of rising bubbles is going to move 150-240 gallon of water an hour...

    There is no simple calculation for airlift pumps as there are so many variables and measuring a zero head flow rate in an airlift it for all intents impossible, but view page 11 of this PDF to get some perspective...

    http://www.bu.edu.eg/portal/uploads/...ift%20Pump.pdf

    From those charts it appears their airlifts were give or take about 5-15% efficient when comparing air volume to water volume, so using those numbers the Tetra 40 might move 1-2 gallons of water an hour if used in an airlift pump configuration? I'm not saying that will be the case here, but still no way I would even hazard a guess that said air pump is moving anywhere near hundreds of gallons and hour...

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    DIYFK member WickedSticky's Avatar


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    Click here to enlarge Originally Posted by Nil13 Click here to enlarge
    you're not going to get 50 gph water from a 20 gph air pump regardless of what other design factors there are in the airlift. Iirc, the ideal air:fluid ratio wrt airlifts is 1:1. So that would be 20gph water ideally...
    Thats all I wanted to verify thank you!

    Click here to enlarge Originally Posted by Meep Click here to enlarge
    ... I said the Tetra 40 rating of an air pump is nothing but marketing nonsense, it literally means nothing...
    I have a water pump rated for 5-10 gallons and an air pump rated for up to 40 gallons, that air pump was the only thing powering my 20L goldfish tank for 5 years until I salvaged a large HOB.
    I didnt think the air pump would be better, but the only numbers Ive seen until now was the "marketing nonsense" tetra churns out, and the fact that the 1.5watt air pump kept my gold fish tank crystal clear and ammonia free would lead anyone to believe the pump is stronger than it seems.

    I tested the air pump flow rate myself using 2 store bought and 3 home made filters the store bought ones moved 4 and 6 gph respectively, the best one I made moved 12.5gph. Question resolved Click here to enlarge

    Thank you both.

    ps I first bought a 150gph powerhead for this tank, this is a cold water tank took three weeks to notice the 8watt water head was heating the water 5-6 degrees. Hopefully the 50gph pump will be good enough and not run hot

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    DIYFK member Nil13's Avatar


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    Click here to enlarge Originally Posted by WickedSticky Click here to enlarge
    I didnt think the air pump would be better, but the only numbers Ive seen until now was the "marketing nonsense" tetra churns out, and the fact that the 1.5watt air pump kept my gold fish tank crystal clear and ammonia free would lead anyone to believe the pump is stronger than it seems.
    You could think that or that people need a lot less biological filtration and lower flow rates than they think they do.

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    DIYFK member Homeslice's Avatar


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    Interesting thread! Question - so it seems GPH on a water pump drives much more water than GPH on an air pump. Which would make sense. But has there been comparisons done as to up-front costs, and watts over time, of the different types of pumps? Air pumps might be relatively inefficient at moving water compared to water pumps, but I think they might be less money up front, and their watt usage seems very miserly. Thanks!

  11. #11
    DIYFK member Meep's Avatar


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    Per WATT airlift pumps (well designed and well maintained) are the most efficient way to move water, but with that efficiency comes low suction, low lift ability, low pressure, inconsistent flow rates and much higher required maintenance...

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    DIYFK member Homeslice's Avatar


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    Can you guys recommend any good air pumps to use for an airlift filter? this would be for anything from a 29 gallon to 75 gallon tank. after doing some amazon research, two that caught my eye:

    https://www.amazon.com/Airmax-PondAi...rch&th=1&psc=1

    https://www.amazon.com/gp/aw/d/B073D...2TL&ref=plSrch

    Both are pond pumps, so presumably they have plenty of power to work for an aquarium. both are reasonably priced, and very low watts - the first one only uses 4 watts! second one 8.

    Thanks for this interesting thread!

  13. #13
    DIYFK member Meep's Avatar


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    The first one is 0.15 CFM the second one is 9 CFM night and day difference in the volume of air they produce...

    As for what you need, it's not all about the volume of air, the design of the airlift pump has to be considered as well, but as a general rule more air is better, as you can always reduce excess air from the pump but you can't magically create more air from the pump...

  14. #14
    DIYFK member Homeslice's Avatar


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    Click here to enlarge Originally Posted by Meep Click here to enlarge
    The first one is 0.15 CFM the second one is 9 CFM night and day difference in the volume of air they produce...

    As for what you need, it's not all about the volume of air, the design of the airlift pump has to be considered as well, but as a general rule more air is better, as you can always reduce excess air from the pump but you can't magically create more air from the pump...

    Oh wow, thanks so much Meep, I didn't pick up on that. So CFM is the best metric to judge them? Seems some give gallons per hour or gallons per second or liters per hour or second, sometimes hard to compare them. It seems that, among those two, the second one is much better, flowing many times more air than the other at only 2x the watts. Any air pumps that you can recommend?

    Also, I'm curious as to the design of the airlift pump and its impact on overall effectiveness. When you mean the design of the airlift pump, do you mean the air pump itself, or the thing in the aquarium (such as some hard plastic tubing) that you attach the air hose to and that the air follows to the top and over? I would have actually guessed that about 99% of it is just getting the air flow in the right place. That is, compare a narrow tube versus a wide tube as an example. Sure, the narrow tube will have a higher air flow, and thus a higher water flow, but that higher flow would be more localized. Conversely, a wider tube would have a lower airflow and thus lower water flow at any one spot, but its flow would be on a wider front, so I would have thought they should equal out overall more/less. Now, if one had restrictions impeding the water getting to the right place I can see a difference for example. Sounds like I'm wrong - any thoughts would be appreciated! Thanks!

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    DIYFK member Meep's Avatar


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    Click here to enlarge Originally Posted by Homeslice Click here to enlarge
    Oh wow, thanks so much Meep, I didn't pick up on that. So CFM is the best metric to judge them? Seems some give gallons per hour or gallons per second or liters per hour or second, sometimes hard to compare them. It seems that, among those two, the second one is much better, flowing many times more air than the other at only 2x the watts. Any air pumps that you can recommend?
    Yes, stated air volume of air (usually stated with no back pressure) is generally the best way to compare them until you get into deep tanks where you will also have to factor in developed pressure because that pressure it needed to overcome the back pressure of the water column...

    Also, I'm curious as to the design of the airlift pump and its impact on overall effectiveness. When you mean the design of the airlift pump, do you mean the air pump itself, or the thing in the aquarium (such as some hard plastic tubing) that you attach the air hose to and that the air follows to the top and over?
    The airlift pump itself, not the air source, efficient airlift pumps have elaborate 'bubbler heads' and orifice designs that create optimal lift far superior to just dropping airstones in a tube...

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    DIYFK member Homeslice's Avatar


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    Click here to enlarge Originally Posted by Meep Click here to enlarge
    Yes, stated air volume of air (usually stated with no back pressure) is generally the best way to compare them until you get into deep tanks where you will also have to factor in developed pressure because that pressure it needed to overcome the back pressure of the water column...



    The airlift pump itself, not the air source, efficient airlift pumps have elaborate 'bubbler heads' and orifice designs that create optimal lift far superior to just dropping airstones in a tube...

    Thank you Meep, sounds like I've got a lot of research/youtube watching to figure out that last point on how to make an efficient airlift pump! Thanks!

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    DIYFK member Nil13's Avatar


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    I'm looking at the second one and it says 16L/min, not 9cuft. The first one converts to 4L/min. 9 cuft would be in the multi hp regenerative blower neighborhood. Liters per minute is what I most commonly see.

    The first one at 4L/min is not anywhere close to an air pump that I would put on a pond. Usually people use at least 20L/min on a pond.

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  18. #18
    DIYFK member Meep's Avatar


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    Click here to enlarge Originally Posted by Nil13 Click here to enlarge
    16L/min, not 9cuft
    Yeah, I blew the math that happens when the wife keeps talking to you about Girl Scout cookie booths, when you are trying to type a reply...

    16l/min = .57 cuft/min still worlds more air than the 1st one...

    And I agree I would not call either of those pond aerators, ponds really need high volume blowers to churn the water, or keep a hole upon from icing over...

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    DIYFK member Nil13's Avatar


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    Haha, girl scout cookies are definitely a worthy distraction.

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    DIYFK member Nil13's Avatar


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    Homeslice, the airlift style being used a lot in koi ponds in Japan and Europe is the Yamabuki airlift. It seems like here in the US, the Deepwater Koi airlift with injector plate at the bottom of a TEE seems to be a little more popular. I haven't had a chance to build one yet, but the short rectangular airlift designed by Wurts at KSU looks like it could be really promising for aquariums and in tank filters. That should give you a good start for the research.

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    DIYFK member Homeslice's Avatar


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    Click here to enlarge Originally Posted by Nil13 Click here to enlarge
    Homeslice, the airlift style being used a lot in koi ponds in Japan and Europe is the Yamabuki airlift. It seems like here in the US, the Deepwater Koi airlift with injector plate at the bottom of a TEE seems to be a little more popular. I haven't had a chance to build one yet, but the short rectangular airlift designed by Wurts at KSU looks like it could be really promising for aquariums and in tank filters. That should give you a good start for the research.
    Thank you Nil13, that will help my research! By the way, I started comparing a few pumps. Here is what I got (I tried to convert all the different metrics to GPH so they would be easier to compare):

    - Doctor Foster and Smith
    - AP-4 (-3?)- $13.59 (after discount code) 28.57 GPH 2.8 watts = 10.2 GPH/watt
    - AP-8 - $23.8 (after discount code) 142 GPH 7 watts = 2.2 GPH/watt
    - Corallife SL-65 - $54 (after discount code) 1030 GPH 66 watts = 15 GPH/watt
    - Amazon - Pawfly MC-3000 - $41.99 - 254 GPH 8 watts = 31.75 GPH/watt
    - Amazon AP-8 - $29.99 142 GPH 7 watts = 20 GPH/watt
    - Amazon Eco Plus 793 GPH - $37.95 793 GPH 18 watts = 44 GPH/watts


    That one at the very end seems like a very good sweet spot - relatively affordable, huge GPH, and the highest GPH/watt ratio of the entire group. Would this be a goo air pump? Would it be too loud? I don't know if to make them efficient they use a different technology that makes them louder or what.

    Thanks!!!

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    DIYFK member Nil13's Avatar


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    The last one is a piston pump instead of a diaphragm pump. I have a similar one and they are only suitable for a dedicated fishroom. They are loud AF.

    I can't really comment on the others since I haven't used them. Although Danner is known to make good pumps and I've heard good things about Periha.

    Just remember that regardless of how loud the air pump is, airlifts are noisy.

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  23. #23
    DIYFK member Homeslice's Avatar


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    Click here to enlarge Originally Posted by Nil13 Click here to enlarge
    The last one is a piston pump instead of a diaphragm pump. I have a similar one and they are only suitable for a dedicated fishroom. They are loud AF.

    I can't really comment on the others since I haven't used them. Although Danner is known to make good pumps and I've heard good things about Periha.

    Just remember that regardless of how loud the air pump is, airlifts are noisy.

    Sent from my SAMSUNG-SM-G890A using Tapatalk


    Thanks Nil13! I was worried about the last one, figured it was noisy. Heard things about Danner as well, will look into the Periha also. Leaning towards trying the Pawfly, 2nd best flow-to-watt ratio, not that expensive, supposed to be pretty quite it seems. In any event even if it sucks I can let the forum know! Thanks!

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