Flow rate or media volume: which is important?

Hi. What is more important in a canister filter: the 4 or 5 times turnover or the bio media volume?
I would guess the media volume.
For sure, a big water turnover isn't adequate if the media is lacking. And what about filters that have a slower flow making for greater and longer contact with the bacteria? Perhaps tank turnover and large filters are not that important.
And if the fish are doing well, as they tend to do, then the insistence on a high turnover via a big canister--is not really a need?

 

Good question. I will be watching and learning with you.

 

Media, shooting water 1000 mph through 1 bio ball won’t work, in a river there’s whole sections which filter the water and keep it pure such as little black water creeks, shooting water 1 mph through 1000 bio balls = more bacteria = more filtration

 

I think you will get people that will advocate from both ends of the spectrum on this topic, but I believe it's a balance of both, the more volume you have the easier it is to grow and maintain your bacteria. The more flow you have the faster you can feed the bacteria and cycle the water.

It also depends on your stocking, if you have fish that need a the higher flow rate to stay healthy and oxygenated, then that would be your factor.

In my opinion, I use higher volume with lower flow rates, as this helps fish stay relatively healthy, not expend energy in the flow, and keep fry/plants from being blown around, and ensures proper contact with the media/bacteria.

With the higher volume, I have the peace of mind if there's a population explosion or if I upgrade tanks, I don't have to worry about getting a bigger filter etc and that my bio load can be handled.

 

Just playin‘ devils advocate here... remember it doesn’t matter how much extra media you have you’ll only ever have as much beneficial bacteria as is necessary to process the bioload

 

I read a crazy study once (I wish I still had the link!) where a dude ran filters with ZERO media and cycled them to the point that they could handle 23 PPM of ammonia in 24 hours. As a result, I'm inclined to advocate more heavily for flow than media.

 

In my tanks I don't need bio media at all, I only use the filter as a water pump, mechanical filtration and to run CO2 reactors.

All the biological filtration is takes place in the substrate, by the plants and with large consistent water changes.

Typically, it's a balance of both. I always recommend a manufacturer claimed 10x turnover rate which roughly = 5x actual turnover rate of the tanks volume. Keep as much or as little bio media in the filter as you wish depending on how heavy or light you are stocking, how much surface are your substrate has, how many / how fast your plants are growing and how often / large your water changes are. Try and keep the biological media near the end of the filtration pathway to avoid the surface area being clogged up with detritus and clean the mechanical media with every water change.

 

As long as there is an ammonia source bacteria will grow. It is going to grow on everything in a tank. Once a tank is well established I believe we could actually remove our filter. Removing it might cause a glitch in the cycle but the bacteria in the tank would quickly replace what has been removed. The main reason for not doing so is a tank does better with some form of mechanical filtration and water movement.

I actually don't think speed of the water flow matters as much as just having flowing water. I run penn-plax HOB filters on my tanks. I can control the water flow. I normally keep it turned down low. The only reason I do so is my fish seem to get stressed with too much water flow.

 

A well designed canister filter will have a suitable media capacity for the design flow rate.

If the flow rate is too high for the amount of media, the water will pass through without adequate mechanical and biological filtration. Always load as much media into the filter as the available space will allow. Empty space in the filter is not doing anything for your aquarium.

If the water flow rate is too low, little water will get filtered and insufficient oxygen will be available to the beneficial bacteria. That can happen if the media gets clogged with debris or the filter intake (especially if you use a prefilter) gets blocked.

Thus, the answer is that both are equally important.

 

There is some significant fluid dynamics to consider here, but I will try to be simple.
Assume in all examples that we have 100 gallons per hour for simplicity.

First, velocity:
If you have a pipe that is 10 inch diameter (78 inch cross section surface area), that narrows to 3 inch diameter (7" cross section surface area) the velocity in the wide section will be 10 times slower than the velocity in the narrow.

10" @100gph= 0.007 foot per second
3" @100gph= 0.075 fps.

Now, dwell time:
If you have a 10" long pipe:
10" dia: .007 fps: 1 minute 58 seconds dwell.
3" dia: .075fps: 0 minutes, 11 second dwell.

Next, we have density of media:
I have done testing based on displacement, I used a square dish and measured the water displaced.
A solid 10" dia piece of ceramic would be viewed as 100% density.

The hollow ceramic rings I use in some of my designs are 40% density

The solid ceramic rings by fluval I decided not to use were 60% density

I also use sponges from 10-30% density from 10-40ppi (course to medium).

Now if we look at our 10" long, 10" pipe as a canister, we can see that depending on what I put in there, the velocity will change significantly, and change the dwell time.
Empty, 100gph, 1:58
10ppi foam, 100gph, 1:48
40ppi foam, 100gph, 1:22
Hollow rings, 100gph, 1:16
Solid rings, 100gph, 0:49

Next we have nitrification rate:
It's fast. I cannot find a solid number but real fast seems to be the consensus.

Well, if it's so fast why did we do the math?
Your filtration will run well up to the point that it "blows clean" and/or "channels". To understand that, you need to understand velocity and it's relation to filter materials and their density.
The following is true if you have a canister, and it's shape or flow rate isn't changing:
A less dense media keeps the water moving slower, is less likely to channel, and will have a better dwell time for first pass filtration (if that's even an issue), but it is more likely to plug evenly(if there is not adequate mechanical filtration).

A more dense media (to a point) can house more bacteria, but it's more likely to accumulate debris in specific places from turbulence caused by velocity and cause channeling.

An overly dense media will obstruct too much volume, cause extreme channelling, and blow clean where there is actual contact due to high/excess velocity.

That said, some filters from the factory come with a large chamber, and low gph coupled with highly dense media. Others have a smaller chamber and faster pump but lower density media. Both can work well if the design is respected. In my wider than required sump design and modified low output fry safe filters, I use ceramic at low velocity. For trickle or higher turn over filters I use sponges. Ultimately, you can get more bacteria on a smaller piece of higher density sponge than most other methods. The turnover rate itself needs to be tailored to your stocking. I would recommend a larger chamber volume for a slower turn over tank to increase dwell time since the water will be spending less time out of the tank and in the filter.


This concept may also help some understand that running testing in the same canister/gph with significantly different density media is not actually a test of the media, but more so the tester and their understanding of fluid dynamics.

 

I think you will get people that will advocate from both ends of the spectrum on this topic, but I believe it's a balance of both, the more volume you have the easier it is to grow and maintain your bacteria. The more flow you have the faster you can feed the bacteria and cycle the water.

It also depends on your stocking, if you have fish that need a the higher flow rate to stay healthy and oxygenated, then that would be your factor.

In my opinion, I use higher volume with lower flow rates, as this helps fish stay relatively healthy, not expend energy in the flow, and keep fry/plants from being blown around, and ensures proper contact with the media/bacteria.

With the higher volume, I have the peace of mind if there's a population explosion or if I upgrade tanks, I don't have to worry about getting a bigger filter etc and that my bio load can be handled.

Agree.

 

There is some significant fluid dynamics to consider here, but I will try to be simple.
Assume in all examples that we have 100 gallons per hour for simplicity.

First, velocity:
If you have a pipe that is 10 inch diameter (78 inch cross section surface area), that narrows to 3 inch diameter (7" cross section surface area) the velocity in the wide section will be 10 times slower than the velocity in the narrow.

10" @100gph= 0.007 foot per second
3" @100gph= 0.075 fps.

Now, dwell time:
If you have a 10" long pipe:
10" dia: .007 fps: 1 minute 58 seconds dwell.
3" dia: .075fps: 0 minutes, 11 second dwell.

Next, we have density of media:
I have done testing based on displacement, I used a square dish and measured the water displaced.
A solid 10" dia piece of ceramic would be viewed as 100% density.

The hollow ceramic rings I use in some of my designs are 40% density

The solid ceramic rings by fluval I decided not to use were 60% density

I also use sponges from 10-30% density from 10-40ppi (course to medium).

Now if we look at our 10" long, 10" pipe as a canister, we can see that depending on what I put in there, the velocity will change significantly, and change the dwell time.
Empty, 100gph, 1:58
10ppi foam, 100gph, 1:48
40ppi foam, 100gph, 1:22
Hollow rings, 100gph, 1:16
Solid rings, 100gph, 0:49

Next we have nitrification rate:
It's fast. I cannot find a solid number but real fast seems to be the consensus.

Well, if it's so fast why did we do the math?
Your filtration will run well up to the point that it "blows clean" and/or "channels". To understand that, you need to understand velocity and it's relation to filter materials and their density.
The following is true if you have a canister, and it's shape or flow rate isn't changing:
A less dense media keeps the water moving slower, is less likely to channel, and will have a better dwell time for first pass filtration (if that's even an issue), but it is more likely to plug evenly(if there is not adequate mechanical filtration).

A more dense media (to a point) can house more bacteria, but it's more likely to accumulate debris in specific places from turbulence caused by velocity and cause channeling.

An overly dense media will obstruct too much volume, cause extreme channelling, and blow clean where there is actual contact due to high/excess velocity.

That said, some filters from the factory come with a large chamber, and low gph coupled with highly dense media. Others have a smaller chamber and faster pump but lower density media. Both can work well if the design is respected. In my wider than required sump design and modified low output fry safe filters, I use ceramic at low velocity. For trickle or higher turn over filters I use sponges. Ultimately, you can get more bacteria on a smaller piece of higher density sponge than most other methods. The turnover rate itself needs to be tailored to your stocking. I would recommend a larger chamber volume for a slower turn over tank to increase dwell time since the water will be spending less time out of the tank and in the filter.


This concept may also help some understand that running testing in the same canister/gph with significantly different density media is not actually a test of the media, but more so the tester and their understanding of fluid dynamics.

That's good stuff.

 

Do we actually know what time bacteria need to convert (oxydize) an ammonia or nitrite molecule into nittrites or nitrates?

 

Do we actually know what time bacteria need to convert (oxydize) an ammonia or nitrite molecule into nittrites or nitrates?

That would be nice to know. Maybe there is someone here that can answer that question.

We know it doesn't take long for the bacteria to catch up with an increased bio-load but we are talking a day or days for that. We also know once a tank is cycled the bacteria must almost instantly remove the ammonia the fish are producing because no matter how many fish (reasonable number of fish) we have in our tank we should never get an ammonia or nitrite reading.

This kinda tells me the bacteria grabs the ammonia as soon as it is brought to it through the filter. If that is the case I don't think it will matter how fast or slow the filter is running. If we have enough bacteria to handle the bio-load no ammonia should get past it.

That doesn't scientifically answer your question though. It is all I could come up with simply through observation.

 

That would be nice to know. Maybe there is someone here that can answer that question.

We know it doesn't take long for the bacteria to catch up with an increased bio-load but we are talking a day or days for that. We also know once a tank is cycled the bacteria must almost instantly remove the ammonia the fish are producing because no matter how many fish (reasonable number of fish) we have in our tank we should never get an ammonia or nitrite reading.

This kinda tells me the bacteria grabs the ammonia as soon as it is brought to it through the filter. If that is the case I don't think it will matter how fast or slow the filter is running. If we have enough bacteria to handle the bio-load no ammonia should get past it.

That doesn't scientifically answer your question though. It is all I could come up with simply through observation.

Going along with this, here is an article that breaks things down a bit of the process:
Behavior and Physiology of Nitrifying Bacteria

All in all, from what I've gathered here, and reading a few articles on the bacteria, Rate + Volume will go together, the bacteria grow up to the amount of food source that exists i.e Ammonia, Nitrites etc, and the amount of oxygen available to them.

If the rate is too low for the bacteria to fully colonize inside the filter, i.e low flow rate will cause there to not be enough oxygen to exist in the filter as well as lack of food source(Ammonia, Nitrite) to feed the bacteria if it isn't being passed through the filter fast enough, then the bacteria will more than likely grow in a place inside the tank(or elsewhere outside the filter) where it can find enough oxygen & food source that is more readily available for it to live and eat.

 

The required dwell for contact at the molecule/oxidation level hasn't been well documented but it's fast enough to not matter as far as I have been able to find. Most of the public study had been based on sewage and waste water treatment but some of it as researched applies to the hobby.

The two easiest sources I use for this are ncbi, and science direct. You will find a wide variety of information. I have read hours and hours of text and the only real timelines I can find that seem fairly consistent are about doubling and population of the colony.

Depending on dissolved oxygen, presence of co2, temperature, and pH, notrosomonas and nitrobacter bacterias can double in colony size as rapid as 7 hours under lab perfect conditions. It is much more common under our normal situations that we see a doubling of the colony as fast as 15 hours for notrosomonas, and 30-50 hours for nitrobacter.

As far as dwell, they find 5 days off hydraulic retention acceptable at solid waste treatment plants but the numbers they are freaking with are apples/oranges with us, and they are actually breaking down solid waste and breaking it down in that short time.

The most important thing I have found in filter design is literally to be mindful of your velocity so you don't blow your media clean. Take it down one extra notch to reduce turbulence/channeling, and you can run it about that fast.

 

Take my Fluval U4 which has thin sponges and that's it. But it's rated for 1000 liters an hour. I guess a high turnover with no hoses and small media content. Probably an accurate representation.

My JBL cristalprofi e901 is similarly rated 900 liters. But of course it's probably moving only half the volume, maybe only twice the volume of 240 liters that I have. BUT it's packed with Siporax.
That aqadvisor calculator gives the Fluval U4 a significant advantage over the JBL. That's according to the notion that the important thing is a circulation of 4 or 5 times.

 

Most breeders and people with large fish rooms use a mainly sponge filters on their tanks.
.

 

Higher flow rate = better mechanical filtration as it can grab the particles faster
More media = better biological filtration, more surface area for the bacteria to colonize on and more contact with the water to help process the biological waste

If you're looking for visualy clearer water you'd want more mechanical filtration with a higher flow rate
If you want biologically cleaner water you would want more media (at probably a slower rate) hence why breeders will be using almost exclusively sponge-filters and Hamburg Matten filters, you want the water to be as biologically clean as possible but not too fussed on visual appearance of the tank

 

Higher flow rate = better mechanical filtration as it can grab the particles faster
More media = better biological filtration, more surface area for the bacteria to colonize on and more contact with the water to help process the biological waste

If you're looking for visualy clearer water you'd want more mechanical filtration with a higher flow rate
If you want biologically cleaner water you would want more media (at probably a slower rate) hence why breeders will be using almost exclusively sponge-filters and Hamburg Matten filters, you want the water to be as biologically clean as possible but not too fussed on visual appearance of the tank

For a breeder tank, you want the tank to be slightly cloudy as the microscopic organisms (often categorized as infusoria) that make the tank cloudy are the perfect size for newborn fish, especially the tiny fry from newly hatched eggs. Some livebearer fry are large enough to accept slightly larger foods, but egglayer fry need even finer foods. Infusoria is the perfect first food.

 

I read a crazy study once (I wish I still had the link!) where a dude ran filters with ZERO media and cycled them to the point that they could handle 23 PPM of ammonia in 24 hours. As a result, I'm inclined to advocate more heavily for flow than media.

I call bull on that

 

I call bull on that

Remember though that the biofilter of a tank includes not only the media in the filter, but any surface in the tank. That includes the substrate, tank walls, decorations, filter tubes and body of the filter, heater tubes, and plant leaves. Thus, even with no "filter media" in the filter, there is still a lot of surface area for development of beneficial bacteria. I suspect that the other surfaces played a far larger role in the biofiltration than water flow rate through the filter. However, good water flow generally means a good dissolved oxygen concentration which is required by the bacteria to do their job. Stagnant water often results in aerobic bacteria activity rather than the aerobic activity of nitrifying bacteria.

 

Remember though that the biofilter of a tank includes not only the media in the filter, but any surface in the tank. That includes the substrate, tank walls, decorations, filter tubes and body of the filter, heater tubes, and plant leaves. Thus, even with no "filter media" in the filter, there is still a lot of surface area for development of beneficial bacteria. I suspect that the other surfaces played a far larger role in the biofiltration than water flow rate through the filter. However, good water flow generally means a good dissolved oxygen concentration which is required by the bacteria to do their job. Stagnant water often results in aerobic bacteria activity rather than the aerobic activity of nitrifying bacteria.

Then there must've been a TON of substrate, decor, plant leaves, etc. so much that there was little room for fish.

If there's no need for filter media, then there's no need for a filter. Toss it and get a simple WaveMaker for water movement. Probably much quieter

 

Then there must've been a TON of substrate, decor, plant leaves, etc. so much that there was little room for fish.

If there's no need for filter media, then there's no need for a filter. Toss it and get a simple WaveMaker for water movement. Probably much quieter

I never claimed that there is no need for filter media or for a filter. The biofilter responsible for the nitrifying of ammonia to nitrite and nitrate is only one part of the water filtration process.

I use a minimum of two filters in each of my tanks, even ones as small as 10 gallons. Yes, it is possible to have an aquarium with no added filtration, but it requires a careful balance with very little animal stocking and a lot of plants.

 

I don't know. I think a balance is good. My best set up is my Aqueon 400 canister. Holds media from my previous canister, the media that came with the new canister, and some I bought and still has room. It shoots water out faster than anything I've ever seen, it's insane to the point that I had to modify the output so that it was more submerged. My other canisters shoot water out pretty good and hold a nice amount of media to, but nothing in comparison. Granted, the bio load is higher on the most efficient one, so, all that wouldn't be necessary.

 

I never claimed that there is no need for filter media or for a filter. The biofilter responsible for the nitrifying of ammonia to nitrite and nitrate is only one part of the water filtration process.

I use a minimum of two filters in each of my tanks, even ones as small as 10 gallons. Yes, it is possible to have an aquarium with no added filtration, but it requires a careful balance with very little animal stocking and a lot of plants.

A careful balance that I wouldn't mess with

 

Then there must've been a TON of substrate, decor, plant leaves, etc. so much that there was little room for fish.

If there's no need for filter media, then there's no need for a filter. Toss it and get a simple WaveMaker for water movement. Probably much quieter

I recommend checking out Father Fish youtube channel. He has many tanks with minimal to no filter media. "Walstad tanks" are another setup without need for any filter media

 

I recommend checking out Father Fish youtube channel. He has many tanks with minimal to no filter media. "Walstad tanks" are another setup without need for any filter media

Walstad tanks have way too much vegetation. I like fish, not that many plants