Are Advertised Flow Rates Bogus?

[MattyM]

I'm doing some research into canister filters, in particular to the Oase Biomaster line. Let's say I'm putting together a 100 gallon planted community tank (70% planted). According to the Oase site, the Biomaster 600 would work. Their site says that this filter is suitable for tanks up to 160 gallons, and has a max flow rate of 350 GPH, that sounds pretty good! I'll inject some CO2, but nothing crazy - just a boost, maybe dropping half a ph point. 

BUT - from what I've found, flow rates could be measured with an empty canister - as in, no media. If so, and I stuff that thing with media, I assume I'd get much less flow than what the specs for this filter say. So... maybe I'd need to size up? 

Is that true? 

[Galabar]

In terms of flow, these folks found that there wasn't much different in biological filtration capacity for a 2X increased flow (canister filters): https://aquariumscience.org/index.php/8-3-1-canisters-in-depth/

If this is true, it may be that water flowing faster over biological media only increases filter capacity by a small amount (to some maximum).

Instead, it might be useful to consider the area of the biological media that you'll have (and attempting to optimize that area with the "best" media).

In terms of flow in the tank, it's easy to create flow with cheap power heads on either side of the tank...

Edited July 3 by Galabar

[nabokovfan87]

On 7/3/2023 at 2:49 PM, MattyM said:

BUT - from what I've found, flow rates could be measured with an empty canister - as in, no media. If so, and I stuff that thing with media, I assume I'd get much less flow than what the specs for this filter say. So... maybe I'd need to size up? 

This is why the common advice is to get the "next size up" when you get your filtration.  The goal is to have adjustability on the flow side or at least a method where you can temper the output flow if you need to.  Eheim is supposed to have info on their website that pondguru is always referencing for stocking recommendations on the filter.  When it comes to certification of products it's kind of a joke that they don't test with a complete unit and the industry really should require better for itself.

Maybe there is a pump / size equivalent you can use off a reference with their data to sanity check the setup.

 

[Galabar]

I wonder if they also test without hoses or restrictions of any kind on the outlet?

[Pepere]

I think you would have to contact the manufacturer to find if listed flow rate is pump flow rate with no head, or with media in canister and hoses and fittings.

However flow rate does not necessarily determine how many gallons the filter is capable of filtering. And neither does cubic inches of space for media, as some media are more effective than other media in terms of practical usuable surface area per cubic inch volume… and of course the bioload of the tank determines amount of filtration needed much more than gallonage of tank.  A schoal of 12 neon tetras in a 125 gallon tank doesnt require much filtration…

Some aquascaping sites call for flow as much as 10 times per hour,, but I dont know that all of that flow has to be filtered flow…. I think you could get by with increasing flow with powerheads or wavemakers to make up what the filter does not provide.  
 

I certainly found noticeable reduction in algae in my tanks from converting to canister filters and spray bars which I am guessing is due to better flow in the tank. Flow dilutes waste organics leaching from tired leaves and ensures plant nutrition is distributed well to all plants better.  I have not achieved 10 times flow in my tanks, but definitely better than before..

most pump manufacturers list pump flow at zero head and no restriction.  It might seem disingenuous, but they have no way of knowing what sort of headloss the pump will be exposed to in you i tended application.

canister filter manufacturers, esp, if the are supplying filter media to use, should in my opinion provide flow rates with their supplied media.  But bear in mind, that as the filter media gets clogged from failing to clean it flow rates will further decrease…

Edited July 4 by Pepere

[Mmiller2001]

I would run 2 600’s on a 100 gallon tank if the idea is to run CO2.

[AndEEss]

I’d run two 850s.

In addition to processing ammonia/nitrite, a filter also oxygenates your water, which helps break down organics. It also helps supply oxygen, obviously.

Most filters put out about 50-60% of what the *pump* can do, with a 5’ head, filter material, etc. Check out the Fluval FX6 page for an example of them listing both.

Edited July 4 by AndEEss

[Pepere]

Again, the height difference between the canister filter and the aquarium water surface imposes very little flow loss.  The weight of the water leading down to the filter adds feet of head to the circulation to offset the feet of head lost pumping back up…  I know,  it is a Bete Noir for me…   
 

I personally don’t see where one needs expensive extra canister filtration though to achieve flow goals. I am open to an explanation how more filtration though achieves better goals than adequate filtration and extra flow via powerheads, wavemakers etc…  I freely admit my understanding may be wrong… Because at 57, I have experienced correction of misunderstandings more than a few times….

Without question though, increasing flow rate in a tank could be achieved far cheaper with a powerhead and spray bar rather than an additional canister filter.  And it is flow and surface agitation that increases oxygenation rather than more filter media… I could see that extra mechanical filtration might yield further benefits..

 

As always I would appreciate corrections and enlightenment of errors of thinking

 

[MattyM]

On 7/3/2023 at 11:00 PM, Mmiller2001 said:

I would run 2 600’s on a 100 gallon tank if the idea is to run CO2.

I was pondering that. How would you place the inlet and spray bars? I saw a Green Aqua vid where they placed an intake and spray bar on each side, pointing at each other. 

[Mmiller2001]

On 7/5/2023 at 7:38 AM, MattyM said:

I was pondering that. How would you place the inlet and spray bars? I saw a Green Aqua vid where they placed an intake and spray bar on each side, pointing at each other. 

I’d go each side intake and spray bar front to back. 
 

As mentioned, 2 850’s would be even better.

[Pepere]

You could easily have an outlet on either side of the tank each feeding alternate ends of a spray bar.  
 

you could either drill more holes or enlarge the holes to allow more flow from it.

Alternatively you could run 2 spray bars one on top of each other, one pointing up slightly to agitate surface for gas exchange, second one running more level to simply increase flow across surface.,

 

Or you could have one at the bottom of the tank to help facilitate return flow.

 

 

[MattyM]

On 7/5/2023 at 8:52 AM, Mmiller2001 said:

As mentioned, 2 850’s would be even better.

Those 850s are like skyscrapers! No way those are fitting under the tank I’m planning but I get the idea, tx!

[Mmiller2001]

Just remember more flow/turnover is better. I run 3 pumps rated at 535gph each on my 120.