# Two canister filter question



## Chrislisk (May 16, 2020)

I currently run two external canister filters on my 240 litre (uk). Is there any benefit to having one full of mechanical filtration and the other dedicated to biological filtration? Currently both are set up with the same and thinking is it better having it separated? If not I'll leave it. Wondered how other people use and run tanks that have two external filters.


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## Deeda (Oct 12, 2012)

I don't see any benefit to having one mechanical only and the other bio only because the bio only one will clog up the bio-media with debris from the tank if there is no mechanical ahead of the bio.

I would just run them as per instructions and it is what I do on my tanks with multiple canister filters.


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## Oscar6 (Aug 4, 2017)

I run multiple cans on several tanks. Concur with Deeda.. use them as intended. For superior mechanical work, I prefer the Aquaclear 110 hob. They move a lot of water, takes literally 2 minutes to rinse the sponge.


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## SenorStrum (Aug 14, 2020)

I LOVE this question, as it allows me to wax Socratic and perseverate.

Why do you need mechanical filtration?
If you do need mechanical filtration, are you using it the correct way?

My answer to the first question is that you don't need mechanical filtration, and if you have it, you're almost certainly using it incorrectly. The idea of mechanical filtration is 2 fold. 
1. You will remove what I'll call "Suspended non-soluble particles." This would be things like the dust from sand I forgot to rinse ... . It seems to me that this type of filtration is necessary after an event or something that causes particulate matter to be suspended in the water. This should not be a common occurrence, so you really shouldn't have to run mechanical filtration on a tank for this reason. 
2. You are using the mechanical filtration to remove poo and uneaten food and such before it breaks down into nitrates. You're doing this wrong. If you're doing it right, you're doing it wrong. Further discussion:

Here, I'll borrow some knowledge from our saltwater friends. They are super concerned about nitrates because water changes are expensive. Bulk Reef Supply, BRSTV on YouTube did an investigation on the use of filter socks in a sump in this capacity. What they found is that filter socks help if you clean them every 3 days. Beyond that, anything trapped in it will break down and wind up as nitrate in the tank. The conclusion - filter socks are great if you're going to do the maintenance. Otherwise they become pointless. 
We can apply this same thinking to the mechanical filtration in the canister. It's not a filter sock, I know, but I believe it still holds. If you want to remove stuff before it breaks down, you're going to be getting into the canister more than twice a week to change out the filtration every 3 days. This is decidedly not a good thing. Every time you open that filter, you increase the likelihood that it will leak. 
Also, if you have it set up to do this, you would have the mechanical before any biological, which means you'll disturb the biological filtration every 3 days which is really also not a good thing.

So, given the above, the non-intuitive answer would be, if you want to have mechanical filtration, set it up in the way you suggest with all the mechanical in one and all the biological in another, and never open that one so as to not disturb it.

However, I don't believe mechanical filtration is at all necessary, and I personally would run both filters full of 20-30 ppi sponge/foam and nothing else and not open them until the water flow slows down.


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## Stu W2 (Nov 17, 2020)

"However, I don't believe mechanical filtration is at all necessary, and I personally would run both filters full of 20-30 ppi sponge/foam and nothing else and not open them until the water flow slows down."

+1

Regards,
Stu


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## Auballagh (Jan 29, 2003)

My Goodness..... it would seem 'El Hefe's ('SenorStrum') quite eloquent written points, have possibly broken this one wide open!  
*applauds*
And I'm going,

*+1*

With an 'alibi'...... 

Yes, I'm THAT GUY who actually runs foam pre-filters on the intakes of just about anything electrically powered in his aquariums. And yes, I'm rinsing and wringing those things out in a bucket with tank water usually once every couple days or so. Those foam intake pre-filters (providing mechanical filtration), seem to extend the periodicity for internal filter cleaning internally by a huge amount! It usually takes weeks before my Aquaclear HOBs need any attention - months before anything is needed for canister filters.


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## noddy (Nov 20, 2006)

I must be missing something. Sponge/foam is mechanical filtration.


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## Oscar6 (Aug 4, 2017)

In my experience and opinion, you are way off Senor. House two large Oscars and a 15in Gibbiceps Pleco together and then tell us you don't need mechanical filtration. Per noddy.. how about those sponges and foam? Or floss or anything that traps dirt, waste, detritus etc. That's the pure definition of mechanical filtration. Doing it wrong you say?? I beg to differ. My Aquaclears take a lot of pressure off my canisters. In my 220 with the O's and the Pleco, I run two Rena xp4 cans and 3 Aquaclear110's. Hob sponges rinsed twice a month. Cans cleaned out at 3 months. None are extremely dirty, nor have reduced flow. I suggest if you wait until filters show reduced flow, you have created a nitrate pump with clogged bio media. Cases for no mechanical filtering? Sure, tiny tanks, wee fish and miniscule bioload. Anything else, in particular the cichlid world, and you need mechanical filtering. My two cents.
.


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## Idech (Nov 8, 2020)

noddy said:


> I must be missing something. Sponge/foam is mechanical filtration.


I was thinking the same thing. Sponges and foams are mechanical and they are indeed necessary.


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## SenorStrum (Aug 14, 2020)

Auballagh said:


> My Goodness..... it would seem 'El Hefe's ('SenorStrum') quite eloquent written points, have possibly broken this one wide open!
> *applauds*
> And I'm going,
> 
> ...


This guy, right here, is NOT doing it wrong. :thumb: :dancing: =D>

However, if you don't remove it after 3 days, that stuff is breaking down, and it becomes immaterial whether it's there or not.

The mechanical filtration (foam prefilters) are being cleaned sufficiently often to remove waste before it is breaking down and creating nitrate in the water. It is NOT being relied on to provide biological filtration. That would be destroyed by squeezing the sponge clean. If you never do this, the sponge gets great biofloc on it that will break down and eat waste in your tank, leaving only nitrate that can be removed with a water change. This is heterotrophic bacteria and not the autotrophic bacteria responsible for nitrogen oxygenation. These bacteria (or archaea if we want to have that argument) are SUPER easy to grow and most folks set this as the very low bar on their biological filtration. "I have no ammonia or nitrite, so my biological filtration is sufficient."

Also, I don't keep Oscars. Or giant plecos. What do you feed them such that their poo has insoluble particles larger than 1mm? The holes in sponge and foam are HUGE. Filter socks are 200 micron pore size. 20 pore per inch foam has a pore size larger than 1mm and 30 PPI is just smaller than 1mm. It turns out that sponges are just really good houses for bacteria, both heterotrophic and autotrophic. The problem here is that the people who SELL you the sponges tell you that it's mechanical filtration AND that it should be replaced. Seems to me like there is a profit motive and not a healthy fish motive here.

I also mentioned "What I'd do." I'd like to point out that this is also what I DID. I did research. Lots of it. I did NOT read "Articles" and other marketing materials from websites that sell fish and fish keeping supplies. Actually, that's not true. I read a ton of them. And I believed them until I read something better. There is a profit motive here, and there is no science here and no accountability. I took all the mechanical filtration (Fine floss and pads) out of every filter I have. I stopped opening them. I got rid of ceramic media, and filled everything with purpose cut foam or pot scrubbers. My tanks (7 of them. Wildly overstocked) all ran perfect. No parameter imbalances, and after the foam broke in (was populated with bacteria) the water was the clearest I've ever seen. The RESULTS were so convincing that I completely changed what I was doing. This was done on 3 30 gallon tanks stocked with 20-25 mbuna each. It is not full grown oscars, which now I'll never get as their feces sounds terrifying. 

Lastly, if you want to know what really works, look to what people do when there is a profit motive involved. What do people do in fish farms? No mechanical filtration. What about municipal water supplies? None. Septic tank systems? Not a lick, just biology taking care of harmful wastes, making them less harmful. Nature is super wonderful, embrace her. What about all the HMFs that are in fish stores? Sponge filters in fish rooms? These are great filters with no mechanical filtration and work great (with the caveat that water must be mechanically forced through them, air is not sufficient for flow in all but the lowest stocking levels).

SO... opcorn:


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## Auballagh (Jan 29, 2003)

Well.... there you have it then. Is 'Senor Strum', 
- Questioning Assumptions?
- Challenging Standards?
- Refuting Norms & Practices?
Heresy I tell you! And, coming from a learned, experienced hobbyist? These sorts of radically wild ideas are Absolutely Terrifying!!!  
Oh no El' Hefe' you've certainly done it now! And feathers (scales?) are sure to be ruffled. 
-
So, to return a biscuit where a bone was offered? The keeping differences between something Mbuna-sized, and just about any Cichlid a foot or more in heavy-bodied length are VERY informative. New World Cichlid keepers can all describe the sight of a contented (ginormous-sized) Cichlid, gnoshing on his pellets, shrimp bits, earth worms, menhaden chunks (Whatever...) and seeing sizable pieces of UNEATEN FOOD launched out of those gill rakers. It's incredibly messy! And a cloud of that stuff just literally goes flying everywhere in the aquarium. The next problem is definitely waste. And, while not exactly terrifying..... the very large Cichlid produces well, very large waste..... products.
And as for the Pleco? Jeeeeze, man. Once they get started on that wood rasping thing they do? I swear a full-sized Oscar would have trouble keeping up with the, errrmmm... 'output', of a Pleco half his size!
Plecos are genuinely notorious for this thing, and are an actual reason why many people choose not to have them in the aquarium.
-
What amazes me, is how truly hard the dedicated Cichlid-keeping crowd works the filtration systems of their tanks. From the purposely over-stocked African type, to the super messy, really big New World types. You gotta admit, the bio-load, feeding amount and toxic mess created in the water, will definitely push aquarium filtration to its limit in our tanks. 
-
_WHY DO WE OVER-FILTER OUR AQUARIUMS? BECAUSE WE HAVE TO._
-
So, I guess I'm practicing a sort of 'Hybrid' model of mechanical filtration for my own tanks. That is, I don't use ANY filter foam inside my canister filters. I just fill them all the way up with matrix rock in a flow-through bag. Two sponges are used for my Aquaclear 110 HOBs (I gave up on other HOB types years ago...). And, some really beautiful levels of Mechanical Filtration provided by the foam pre-filters on the intakes of ALL my filtration systems (even one sump). With each of those pre-filters rinsed out usually three times per week.
I dunno... works great for me. But then again, I'm pushing over 80 percent water changes weekly through a couple of those tanks to keep Nitrates below 20 PPM. :roll:


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## SenorStrum (Aug 14, 2020)

What am I supposed to say here?

Tus peces están demasiado grandotes. 

Allow me to clarify my point slightly - if uneaten food (get mbuna, this doesn't happen  ) finds its way into the filter, or if the notoriously ginormous poo does the same, if it's not pysically removed from there within 3 days, it breaks down to nitrate anyway. If one wants to keep nitrates low, these types of things must be removed from the high-flow area and now allowed to break down. If it's trapped in the filter floss, there ain't S-- ...stuff... in the world, pre or post eaten, that will survive for two weeks.

I know for a fact, and this is mostly because I have a lot of experience in the subject, that I'm not going to change the mechanical filtration every three days, so I plan for not doing it, and I don't fool myself. I KNOW that not removing physical waste mechanically is going to create more nitrate in my tanks which must be removed. Auballagh, if you're actually cleaning the pre-filters 2-3 times per week, you are actually accomplishing this goal, which is VERY rare.

So, my main point to OP was to decide whether or not you're going to clean them frequently enough to accomplish the goal you're setting out to accomplish. If you're not doing that correctly, there are deleterious effects on the other goals.

Now, I'll throw in just a few more data points: I'll discuss the locations of both my money and my mouth. I DO actually run filter socks on my main aquarium. 4 7x16 filter socks, actually. The only reason for this is because I ordered the sump with it before I had learned the above and removing them is VERY loud. In ALL tanks where I have canisters, I have them full of foam, no mechanical at all. I offer this, simply to say that I believe what I'm saying.

What is really interesting to me is that folks are throwing out blackwater fish and talking about filtration but there is no mention here whatsoever about using filtration to manage the bacteria in the water column to comply with the immunological needs of blackwater fishes and avoid HITH and other diseases to which they are prone. Hard water cichlids, FTW!


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## Chrislisk (May 16, 2020)

So what you are saying is get rid of all my ceramic media and fill my canisters with sponges and foam? Really?


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## Stu W2 (Nov 17, 2020)

IMHO it would benefit all aquarist, young and old, to read the linked site through several times over. Many of the most entrenched hobby beliefs are challenged. Successfully in my view.

https://aquariumscience.org/

Regards,
Stu


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## Idech (Nov 8, 2020)

Stu W2 said:


> IMHO it would benefit all aquarist, young and old, to read the linked site through several times over. Many of the most entrenched hobby beliefs are challenged. Successfully in my view.
> 
> https://aquariumscience.org/
> 
> ...


It would be more appealing to read if the author of the website had a name. It is rather suspicious that they won't name themselves.


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## SenorStrum (Aug 14, 2020)

Hi Idech, 
Yes. I'm telling you exactly that. After reading Aquariumscienc.org, I made the change you suggest. I changed my mind entirely. ALL my little fish tank problems went away. My water got super crystal clear. All the little issues that my fish seemed to be fighting off went away. There are absolutely no nutrients imbalances or anything but nitrate detectible.

I simply do not understand the argument that the information aggregated into that website is bad because you don't know who aggregated it. I decided to take the information at face value as presented because it's all linked to actual studies that one can find for themselves, just from the internet. Also, I find the author's candor to be extremely refreshing. It's one of the major reasons I trust what he says. After running a test of biological media, "Dave" writes:

"A Confession
The author would like to be able to say he knew what this testing revealed all along and has been using 100% pot scrubbers in all his many canisters over the 53 years he has been keeping aquariums. That would be a lie. For 53 years the author has used a combination of all the media that came with a canister, a ton of a huge variety of media which was on his garage shelving, and media he bought. Most of his canisters were filled with a pretty random combination of Matrix, ceramic rings, lava rock and bioballs.

The author simply felt that the media in a filter wasn't very important and they were all pretty much equal. The author was wrong, dead wrong. Whoops!"

I find that it's a lot easier to believe than the fact that ceramic has 17,000 times the usable surface are, being promulgated by the very people who make and sell this ceramic media. There are no links to anything to purchase on aquariumscience.org. There are no ads. There is nothing but well laid out information with their sources for the reader to take or leave. I frankly think that this is much more trustworthy place to get information than somebody who has a profit motive.

One of the major points throughout the articles is that shooting only for zero ammonia and zero nitrites is setting a very low bar for the health of the aquarium and fishes. Ceramic media absolutely will do this.

However, ceramic media maker's claims that the INSIDE has a ton of usable surface area are extremely over-inflated. Indeed, I tested it. I went and found any used ceramic media, and I got a baby-medicine doser (syringe) and tried to force water through it with the plunger. Could not be done. This means that water under virtually no pressure inside a filter is NOT flowing through the media, but instead around. Therefore, you are down to only the surface area of your ceramic media being in any way useable for nitrogen oxidization or housing of the heterotrophic bacteria that are actually keeping the aquarium water clean. So, since we all can agree that the bacteria (and archaea - not going to have that argument) which are healthy for your aquarium are only found on surfaces, and, on it's face, ceramic is not as advertised because water won't flow through used ceramic, one should logically switch to something with more useable surface area - like sponge or pot scrubbers.


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## Rhinox (Sep 10, 2009)

Stu W2 said:


> IMHO it would benefit all aquarist, young and old, to read the linked site through several times over. Many of the most entrenched hobby beliefs are challenged. Successfully in my view.
> 
> https://aquariumscience.org/
> 
> ...


Wow this is like the tvtropes clickhole of fishkeeping. I just get lost for like 2hrs in an eye blink. Diving back in now, pray for me! Lol


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## Idech (Nov 8, 2020)

Hello SenorStrum,

I agree the information on the website looks very valuable, but it would be more credible with a name. As for pot scrubbers, I'm not against it at all and I've thought about trying it in the past. I haven't bought ceramic rings or bio balls in 15-20 years. Those I have came with the canisters I bought and I just kept them. Once your cycle it's going, it's kind of a pain switching for a different type of media because it has to be done in small steps.

I've also been considering biohome media, but it costs and arm and leg and you need tons of it. There's a similar media you can buy in lieu, I forgot the name. So yeah, life isn't all about ceramic !


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## SenorStrum (Aug 14, 2020)

Hi Idech,

I read through Biohome's website. I'm guessing that you are hoping to reduce Nitrates as the site suggests is possible? Long story very short, it's not possible without a pretty complicated rig to reduce nitrates. There is a sticky thread on MFK about this. The reduction of nitrate through anaerobic/anoxic means requires the addition of a carbon/carbohydrate source. If you're not dumping vodka or sugar into a specially designed reactor chamber and running water through it very slowly, you will not accomplish denitrification, so I'd highly suggest you save your money.

IF it were possible to do this, my tank would be doing it. I have 700 pounds of lava rock in there. Much of it had been cycled with seachem stability for months in the garage in my rock box. It's just not really scientifically possible to reduce nitrates this way at home. That being said, this is also a change of mind for me. I'm telling you it doesn't work, but I used to believe the internet that said it would. So I tried it. I spent the money on stability. I got the lava rocks... nothing. Absolutely no reduction in nitrates. And then I found aquariumscience.org and learned why it wasn't working. Then I had to admit that seachem just wanted my money, and I was a bit of a fool and gave it to them.

Lastly, I would guess that biohome would suffer from the same problem that all of the "fancy" medias have. They all rely on extremely small holes and structures to increase the surface area. The holes plug up, water won't flow through it at all, and then you're left with nothing but surface area. Plus, to your point, it's SO expensive!


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## Idech (Nov 8, 2020)

SenorStrum I have doubts also about the biohome, which is why I haven't bought it. But there are quite serious fish keepers who've tried it and talk about it on Youtube. It looks tempting.

But for now, I only have 5 ppm nitrates in my tank so that would be a waste of money.


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