A Challenging Question on Bacteria . . .

[Wy Renegade]

Two points here that I want to weigh in on briefly. I'll come back and hit more points when I get home from work.

I disagree with this. You're thinking to much about volume and not enough abut surface area. I looked up the surface area of the ceramic "Ehfisubstrat" that came with my canister filter, and it is marketed at about 20,000 square feet per gallon. I have about 3L in my filter (more than the 2L that it comes with). So, after some quick math, my little 2217 has just under half an acre of surface area. All/most of that surface area is readily supplied with nutrients and oxygen by the flow of the filter, meaning that the bacteria colonies can be larger and more robust. Compare that to the substrate where only the top inch or so is really supplied with nutrients. Low layers would still have aerobic bacteria, but they won't be thriving like the upper ones would be, and even those bugs envy the life of filter-bacteria.

Ah, welcome my friend, I was hoping that you might join the discussion. Like yourself, my participation will have to end soon, but I will be checking back in later to continue the discussion.

So to your point, let me simply ask this, what is the total surface area that exists within the top inch of say your aquarium given your substrate. No idea if your tank contains either sand or gravel, yet given the larger volume of gravel or sand within that area, if you calculate the actual surface area (which in an adequately filtered aquarium should have the same flow/oxygen levels/etc), I have a hard time believe that the actual surface area will not be signicantly higher. We cannot factor in the porousity of the ceramic media while excluding the either the porousity of the sand or rock, nor the grain size which creates more surface area within that volume, can we?

I really don't think that the water in filters is especially oxygenated. Maybe some filters (biowheels), but it seems like most of mine only have water/air contact right before the water leaves the filter. My AC is certainly this way.

Agreed, indeed the flow generated by the filter itself should adequately distribute said oxygen evenly without and in little to air contact is made within the filter itself.

The second thing is something that has intrigued me for a long time, and that is the role of phytoplankton in our ecosystems. They are present in both salt and freshwater, and they have to be getting their nitrogen from somewhere. So while I due doubt that bacteria has a major presence in the water, I would imagine that there could be a whole host of other organism, autotrophic or otherwise, floating around that could also make use of nitrogenous byproducts. I find it hard to believe that there is only one organism that can make use of a single, readily available resource like reduced nitrogen. We see this in plants as well.

Indeed this is true, however keep in mind that the term phytoplankton is in and of itself some ambigous; phytoplankton includes not only protists, but bacteria and algae spores as well as full blown microscopic algae, all of which are involved in the uptake of nitrogen at all times. Green water anyone? Dioflagellate bloom perhaps?

For anyone that is interested, the cloudy water we see is from (if I recall correctly) heterotrophic bactceria. Our nitrifying bacteria are chemotrophs.

No, no I don't think so. Our nitrifying bacteria are autotrophs, but they are definitely not chemotrophes (if they were we would have to have many chemical reactions occurring and chemical gases being released within the aquarium that we have absolutely no interest in). Perhaps you confused your terms?

I don't think anyone is arguing that there is no bacteria in the water column. It's just that there is a ton more attached to surfaces. Think about your garbage can. You can sanitize a trash can and put sanitized food in it, and if left unsealed out in the open, it will begin to mold, rot, and whatnot. Thats because all of those fungi and bacteria and god only knows what else are everywhere. They're even in the air you breath. In fact, I bet you just sucked some in just now! But compared to on the surface of about anything, there's a trifling amount. But you certainly wouldn't eat a decomposing sandwich.

Oh good, then perhaps we can lay the old wives tale that nitrifying bacteria does not exist within the water column to rest? I certainly agree that there is substantually more to be found on surface areas than in the water or in the air, but they do also exist within both places (or at the very least their endospores do)

An additional concern: It is entirely possible that bacteria will not multiply properly (or quickly) without an attached surface. Much of the bacteria in water will come from established colonies on a surface somewhere. The bacteria breaks off and floats along until it finds another surface. Many bacteria (not sure about out nitrifying bacteria) have life cycles like this.

Indeed I can agree with this very readily, I would add only the likelyhood that endospores from existing bacteria colonies are also most likely released into the inhospitable environment of the water column. Upon being provided with a suitable surface such bacteria are sure to begin growing and colonizing all available surface areas with viable conditions.

 

[slitherbomb]

While I personally agree with you on the existence of such bacteria within the water column, I have to say that I do not think that they are found within the water column in signicant enough ammounts to allow for the full establishment of a entire aquarium just based on water. Can you please give us more information on the stocking levels and methods you employed?

Ok this is with the biocube(first saltwater tank)

Bought the biocube, and some dry sand from Petco. Setup the tank in my room then filled with water I gathered from outside with a bucket. Waited for it to settle(the sand) and then I put in a small striped burrfish (~1 in), 2 random minnows I caught, and 2 chromis (bear in mind that this was before I knew about tank overstocking). About 2 days later I purchased the API liquid test kits (ammonia, nitrite only) and tested the water for those. The tests came up with 0 on both and I tested for about 2 weeks straight and by then I thought my kit was expired so I took it to my Lfs, and they got the same results. I then purchased cured live rock that day.

 

[Wy Renegade]

Hi a very interesting thread this. Now before i start i am certainly no expert and certainly hardly ever use test kits. All assumptions are based on many many years of experience.
First off, bacteria do live almost every where inside the aquarium,hence why i never advocate over cleaning the decor if at all! The bacteria thrives more in the filter simply because the surface provided by the sponge,sintered glass media is more to there liking,with a constant supply of both oxygenated water and food for the bacteria? As for seeding another tank with water or substrate from a mature tank will help but as already said will not provide an instant cycled tank. A lesson i learnt not long ago was very interesting and only thanks to a more knowledgeable fish keeper helped more sort it out! I dissmantled a six foot tank and placed some of the fish into a four foot set up with the filter,wood substrate decor etc,so my theory being the tank would be instantly cycled,so proceeded and all went well,but the tank took nearly six months to settle? The problem was that although the filter was mature as was the water,decor etc,because the tank was now smaller with a lighter bio load the bacteria had to readjust hence the tank remaining looking 'murky' until the bacteria had readjusted? Also Simon me mate up the local fish shop also agreed with me in that the bacteria levels in an aquarium are only as numerous as the amount of food {fish waste} available to them,so when we place new fish into the aquarium they have to multiply to compensate,which may only take a day or two,hence why we should never put to many fish into a tank and leave it at least a fortnight between getting new fish?
External filters are very good but trickle filters where the water is more exposed to the air will be more efficient in my opinion.
Also the idea that most of the bacteria is in the substrate is why we used to use undergravel filter plates,but as they blocked they became very inefficient,as they are much harder to clean than standard filters such as externals and internals.
Footnote how do they measure or come up with what is supposed to be the surface area of sintered glass media such as eheims ehfisubstrate?

Some interesting observations and explainations, and if I understand correctly for the most part agrees with what I'm saying. Interesting however that you note that a reduced fish load in a smaller aquarium took more time to establish. I wonder if the release of debris/nutrients from the transfer of the substrate may have had something to do with that.

 

[aqua_chem]

Indeed the part about then not actively seeking it out is quite true. And yet I must question the assumption that the filter somehow receives more flow. Isn't true that the filter is presumidly turning over the entire water volume of the aquarium? Often times in the space of only hours or even an hour? If this is true, then all the water within the aquarium would not only be exposed to the surface of the filter media, but also to the surface of the substrate. If this were not the case then within the aquarium one would have to expect to find areas of water significantly higher is dissolved nutrients as they failed to be filtered the same as other areas, and as a result we would have to expect to see differeing results from ammonia, nitrite, and nitrate tests taken on water from different areas of the aquarium. True? Personally, I've never found that to be my experience. So I must conclude that all water within the little glass box is moving in a very similar fashion and therefore both substrate and filter get the same exposure to oxygen rich water and to nutrients.

I think we're all forgetting about diffusion here. You don't need movement for any chemicals to equalize across a tank. Even slight, insignificant flows will eventually even out concentration levels across a tank. The only thing that could cause pockets of any sort of chemical would be an active uptake/release of a chemical, ie, lower CO2 levels in the middle of plants.

 

[bruinsbro1997]

Interesting thread. I would like to know some more about bacteria and such. Subscribed and following!

 

[eco23]

Wait, wait my friend. If we are going to allow personal experiences as proof in this thread (which I certainly agree that we must for the sake of our discussion, and that certainly is the point from which you are presenting your evidence), then we must give all personal experiences the same weight and the same respect. It is not fair of you to dispute someone else's experiences when asking others to accept your experiences as proof positive. You also ignored my earlier statement in which I stated I've seeded freshwater tanks with water (actually many times). Does that mean that these tanks were fully cycled and ready to fullly stock? Not at all, but the "seed" populations were there and the bacteria populations were able to begin growing from there.

There's a difference between questioning / having concerns about statements which go against accepted methods and extensive experience by hobbyists...compared to practices which are accepted as the norm and have consistent results. Again though, SW tanks are a foreign concept.

No one said there was no BB in the water column, the belief and research shows there are negligible amounts. If I had a sterile tank, would I take water from an established aquarium? Sure, no harm done...but honestly I'm not sure it would make any measurable difference.

So you are saying that donating filter media to a newly established tank allows for the full stocking of said newly established tank? I hardly think so, unless you are donating the entire filter. Certainly discussion here as well as on other forums, as well as personal experience will not bear that out. As far as "seed" material, I agree. But how much seed material are we talking when someone talks about moving substrate? or decorations, or even water. Has anyone ever donated half the sand substrate out of their aquarium to a newly established tank?

I never once used the word "fully", but yes, you can stock a tank with fish immediately after donating a sufficient amount of media. For example, I recently had 7 Tetras in a 10 gallon QT for 3 weeks. I simply set up the QT with bio-media removed from my canister. I performed water changes 2x a week like I do with all my tanks...but during the 3 weeks they were in there...there was no cycling, no toxins. The proportion of bacteria : fish was sufficient to handle the bio-load. It's the same method most of us use to set up new aquariums. Even though I'm considered like the fishless cycle guy on the site...I've only done it on new, sterile aquariums when no seeding material was available. (not counting a few times I've done it for the purpose of experimentation)

 

[Wy Renegade]

Ok this is with the biocube(first saltwater tank)

Bought the biocube, and some dry sand from Petco. Setup the tank in my room then filled with water I gathered from outside with a bucket. Waited for it to settle(the sand) and then I put in a small striped burrfish (~1 in), 2 random minnows I caught, and 2 chromis (bear in mind that this was before I knew about tank overstocking). About 2 days later I purchased the API liquid test kits (ammonia, nitrite only) and tested the water for those. The tests came up with 0 on both and I tested for about 2 weeks straight and by then I thought my kit was expired so I took it to my Lfs, and they got the same results. I then purchased cured live rock that day.

Indeed. And what may I ask was the volume of the biocube?

 

[Wy Renegade]

I think we're all forgetting about diffusion here. You don't need movement for any chemicals to equalize across a tank. Even slight, insignificant flows will eventually even out concentration levels across a tank. The only thing that could cause pockets of any sort of chemical would be an active uptake/release of a chemical, ie, lower CO2 levels in the middle of plants.

But isn't it true that the random slow movement of particles through the process of diffusion is easily outpaced by directional flow? While equilibrium through diffusion would occur in a stagnant body of water, I find it far more likely that equilibrium within the aquarium is maintained by water flow to a much greater degree.

 

[Wy Renegade]

There's a difference between questioning / having concerns about statements which go against accepted methods and extensive experience by hobbyists...compared to practices which are accepted as the norm and have consistent results. Again though, SW tanks are a foreign concept.

Agreed . . . that said however, much of the information that I am challenging here goes against the accepted methods and extensive experiences of many prior hobbiests (prior as in no longer around to particpate in this forum). Many of whom kept wonderfully successful aquariums over many, many years. I agree that mixing and matching information from both SW and FW aquariums does somewhat cloud the information, perhaps it would have been best if I had refrained from bringing the saltwater into the discussion, but I'm not fully convinced of the fact that we are truly talking about two completely different animals (or bacteriums in this case).

No one said there was no BB in the water column, the belief and research shows there are negligible amounts. If I had a sterile tank would I take water from an established aquarium? Sure, no harm done...but honestly I'm not sure it would make any measurable difference.

How do we define negligible in an organism capable of producing 50,000 billion, billion offspring in a day? I would have to say that if there were even one viable bacterium within the water column it would have to make a measurable difference.

I never once used the word "fully", but yes, you can stock a tank with fish immediately after donating a sufficient amount of media. For example, I recently had 7 Tetras in a 10 gallon QT for 3 weeks. I simply set up the QT with bio-media removed from my canister. I performed water changes 2x a week like I do with all my tanks...but during the 3 weeks they were in there...there was no cycling, no toxins. The proportion of bacteria : fish was sufficient to handle the bio-load. It's the same method most of us use to set up new aquariums. Even though I'm considered like the fishless cycle guy on the site...I've only done it on new, sterile aquariums when no seeding material was available. (not counting a few times I've done it for the purpose of experimentation)

Excellent! Now let me throw some of my own experiences at you. I've set up literly dozens (no, I'm not exaggerating ~ we tear down and reset aquariums on a yearly basis) of aquariums over the years that I've participated in this hobby. In almost every case, we've transfered vacuumed water from the substrate from established aquariums into the newly reset aquariums (new substrate, new water, etc.). We then replaced the fish into the newly reset aquarium (all of which are lightly stocked for their water volume), tested the water daily for several weeks, performed regular maintance water changes, and in almost every one of these cases, experienced no toxic spikes in ammonia or nitrites. If you speak to pet store owners as well as other old school hobbiests, they will tell you the same.

 

[slitherbomb]

Indeed. And what may I ask was the volume of the biocube?

It's the 14g biocube, but many people say that actually water volume is close to 10g.

 

[Donkey Gun]

apologies for my newbie question, but what do guys mean by seeding tanks?

 

[eco23]

apologies for my newbie question, but what do guys mean by seeding tanks?

Moving beneficial bacteria from an established aquarium to a new one in order to help develop the bio-filter (colonies of good bacteria which convert the toxins produced in the tank).

The definition of what is considered efficient seeding material is basically the topic of discussion . The commonly held belief is that your filter material harbors the vast majority of this bacteria compared to other surfaces in the aquarium. That's what's being debated (although I'm starting to lose sight of the initial question).

 

[Wy Renegade]

It's the 14g biocube, but many people say that actually water volume is close to 10g.

Indeed, so five very small fish in 10 gallons of ocean water correct? If I may ask, what is a minnow from the ocean?

Moving beneficial bacteria from an established aquarium to a new one in order to help develop the bio-filter (colonies of good bacteria which convert the toxins produced in the tank).

+1

The definition of what is considered efficient seeding material is basically the topic of discussion . The commonly held belief is that your filter material harbors the vast majority of this bacteria compared to other surfaces in the aquarium. That's what's being debated (although I'm starting to lose sight of the initial question).

Really? Why? we're talking about about viable bacteria populations found on other surfaces than the filter media are we not? The water column and the substrate?

 

[Donkey Gun]

That's what I thought, but wanted to be clear. Well, I've been instructed to change my filter once a month.. if most of the bacteria lives on the filter, then why have I not seen toxic spikes every month?

Also when I upgraded to a larger tank, I seeded it with the old rocks and and plants from the smaller tank. In addition I added a bacterium starter kit, Let it run for a week, and then added the fish. Never any problems that I could test or see. So it would be my opinion that most of the bacteria is in the water column and substrate.

 

[Wy Renegade]

That's what I thought, but wanted to be clear. Well, I've been instructed to change my filter once a month.. if most of the bacteria lives on the filter, then why have I not seen toxic spikes every month?

Also when I upgraded to a larger tank, I seeded it with the old rocks and and plants from the smaller tank. In addition I added a bacterium starter kit, Let it run for a week, and then added the fish. Never any problems that I could test or see. So it would be my opinion that most of the bacteria is in the water column and substrate.

Do you totally change out all your filter media? Again personally I would argue towards the substrate, but that is part of what we are discussing.

 

[eco23]

Really? Why? we're talking about about viable bacteria populations found on other surfaces than the filter media are we not? The water column and the substrate?

As I said, perhaps I'm losing sight of what this thread is really about. Are we debating the viability... or the proportion of BB in the filter media vs. elsewhere?

I think every one of us knows that the nitrifiers are found on every oxygenated surface of the tank, no debate there. If we're talking about viability in the sense that filter media is more efficient in cycling a tank based proportionally on the sheer volume of bacteria in media vs. other areas or water...I'm honestly surprised it's still a question.

I love threads like this because when questions are asked, especially ones that defy common belief, it leads to more answers and new information. That said, I am surprised this is the topic of discussion.

I'm glad the previous poster had success with his method, but I think we can mostly agree that is not the norm. The facts that we do know definitely seem to support what is considered and repeated as common knowledge in the hobby.

-Nitrifying bacteria are primarily surface adherers...though we can agree there will be some % in the water column if for no other reason than becoming dislodged

-Knowing what we do about their needs for efficient colonization, it appears filter media is the most hospitable environment for them for numerous reasons.

-Example after example of people donating established media compared to donating gravel and other items. Every single day I'm messaging with members (many of whom have never posted) during cycling. I've seen the efficiency of filter media compared to water / other items both in my own tanks as well as countless members

-Tons of testament from members that changing substrate has minimal impact on the bio-filter, while we see new members all the time having mini-cycles from replacing filter cartridges and other types of media.

-When someone upgrades to a larger tank, they can simply move the existing fish and filter to the new tank, and besides the small potential (rarely seen IME on the site) for a mini-cycle due to the loss of bacteria on other areas...we don't hear negative consequences. I believe there's not one of us on this thread who would advise another member just to move over all their fish, water and substrate and consider it cycled, or virtually cycled like it is by moving over the established filter.

 

[adeebm]

I would point out first of all that regardless of available oxygen and food, bacterial colonization would still be limited by the availability of space. Additionally, I would point you back to my earlier responses (posted after you posted your comments) in regardes to equitable distribution of oxygen throughout the aquarium provided adequate flow.
If indeed one can argue for the fact that water flow through a cansister filter can provide adequate oxygen levels for bacteria, cannot the same argument be applied to the water flow through the gravel? Water does not circulate independently through different areas of the aquarium (for the most part). Rather circulation is generated by the filters and is generally fairly evenly distributed throughout the aquarium (excepting flow deprived areas such as deep within the substrate or deep within the rock).

Yes, bacterial growth is limited by space. If you look at population growth models, what's termed as the carrying capacity, or maximum poluation would here be defined by the available surface area. If you compare gravel to ceramic(or other) biomedia, you will see a vast difference in surface area. Gravel is basically spherical, and has a surface area of 4pir^2. Biomedia on the other hand, is engineered to have an enormous surface area for its volume, which is the point of biomedia. Is there flow through gravel? Yes there is. It is however far less than the flow through a filter. That combined with the low surface area of gravel is why a filter is much more efficient at holding a population of bacteria. There is no denying that the gravel and all surfaces of the tank are colonized, but groth factors will dictate exactly what the population per volume is.

Ah, and now we begin to get at the crux - thank you my friend. Isn't it also true that the same denitrifying bacteria are found within the LS base of the saltwater aquarium as are found within the LR surface area? In fact the original tanks running deep sandbed were successfully run without any LR at all were they not? Now keep in mind that flow in and of itself does not necessarily provide for oxygenation, surface aggitation is also required so that oxygen can enter the water in the first place. But again I ask the question, does the HOB filter truly move the water across it independent of the rest of the water within the aquarium or does it not move all the water within the aquarium to that rate of flow?

Flow is volume over time. If say a filter is rated for 160gph, 160 gallons of water pass through the filter media in an hour. This is significantly more than what passes through an equivalent volume of gravel or sand. This is especially tru in FW where the use of powerheads is often not employed.
As for the dentrifying bacteria you are talking about, that is an entirely different beast. Dentrifying bacteria convernt nitrates into N2 gas, in order to utilize the oxygen bound in NO3. Denitrfying bacteria are anaerobic, and are found in conditions lacking oxygen. They are often relied upon in SW systems to maintain 0 nitrates, since in SW even small amounts of nitrates can be devastating to coral. These bacteria live deep within liverock, and at the bottom layer of a deep sandbed. As water flows through the LR or sand, it is stripped of oxygen by the nitrifying bacteria. By the time it reaches the deepest parts, there is little or no oxygen left. This is where the denitryfying bacteria live, and because of the lack of free oxygen, extract oxygen from NO3 molecules.

Tanks without LR but with a DSB may be succesful, but will not be able to handle the same level of bioload is those with LR. These systems often rely on heavy use of protein skimmers to remove DOCs before they can decay. Even then, the lack of LR will limit stocking capacity. You can run an FW system without an HOB if you wanted to. Get a 55 gallon with a powerhead or two and lots of gravel. Cycle it, then drop in a few guppies. The gravel will be able to handle it. However, your bioload capacity will be limited and if you want large schools of fish, you will need to increase your bacterial capacity with filters.

With bacterial populations, it all comes down to available space and nutrients, as with any population. Space determines the maximum capacity, and the availability of nutrients(oxygen, ammonia, etc) will determine the exact population. That's all you need when comparing the efficiency of different medias/surfaces for bacterial growth capacity.

The bacteria in gravel is, Im sure, an important factor in keeping ammonia levels down. But on a per volume basis, an HOB filter is far more efficient. If I have a filter with a volume of one gallon, or one gallon of gravel, which do you think would be able to process more ammonia?

--Adeeb

 

[aqua_chem]

We should get a batsign or something of the sort for when these conversations begin so that I can get to the party on time!

So to your point, let me simply ask this, what is the total surface area that exists within the top inch of say your aquarium given your substrate. No idea if your tank contains either sand or gravel, yet given the larger volume of gravel or sand within that area, if you calculate the actual surface area (which in an adequately filtered aquarium should have the same flow/oxygen levels/etc), I have a hard time believe that the actual surface area will not be signicantly higher. We cannot factor in the porousity of the ceramic media while excluding the either the porousity of the sand or rock, nor the grain size which creates more surface area within that volume, can we?

Ok, napkin math!

Let's model a gravel substrate of negligible porousity (which i think is pretty reasonable for many aquarium gravels) as being composed exclusively of perfect spheres packed together in closest packed manner. Packed like this, about 75% of the volume is occupied by spheres. Thus, if we divide by the volume of a sphere (4/3 π r^3) we get the total number of spheres, and if we multiple by the surface area of a sphere (4π r^2) we get:

SA = 2.25 * A*(d/r)

Where A is the area (footprint) of your tank, d is the depth of the substrate, and r is the radius of your spheres. For these calculations, I'm only using a depth of 1" for substrate, as anything more than that doesn't have appreciable bacteria levels. Assuming a 3mm diameter of aquarium gravel (a popular size), and using generous footprint (40breeder), I get the total available surface area to be....

About 171.5 square feet. Compared to the 15000 square feet from Ehfisubstrat (which is actually closer to 1/3 an acre), that's about 1%.

Indeed this is true, however keep in mind that the term phytoplankton is in and of itself some ambigous; phytoplankton includes not only protists, but bacteria and algae spores as well as full blown microscopic algae, all of which are involved in the uptake of nitrogen at all times. Green water anyone? Dioflagellate bloom perhaps?

If anything is using the nitrogen in the water column, I think that it would be these guys. I really think that the various fauna in the water column might have a surprisingly profound impact on our aquariums' ecologies.

No, no I don't think so. Our nitrifying bacteria are autotrophs, but they are definitely not chemotrophes (if they were we would have to have many chemical reactions occurring and chemical gases being released within the aquarium that we have absolutely no interest in). Perhaps you confused your terms?

I'm pretty positive on this one. Nitrifying bacteria get energy by oxidizing reduced forms of nitrogen. I believe the technical term for them is chemolithotropes. They are technically autotropes (specifically chemoautotropes), but definitely chemotropes. They are definitely not phototropes, which most people associate with autotrophy.

Oh good, then perhaps we can lay the old wives tale that nitrifying bacteria does not exist within the water column to rest? I certainly agree that there is substantually more to be found on surface areas than in the water or in the air, but they do also exist within both places (or at the very least their endospores do)

...

Indeed I can agree with this very readily, I would add only the likelyhood that endospores from existing bacteria colonies are also most likely released into the inhospitable environment of the water column. Upon being provided with a suitable surface such bacteria are sure to begin growing and colonizing all available surface areas with viable conditions.

In terms of sheet numbers though, there are probably millions of more bacteria on surfaces than in the water column. Keeping in mind that bacteria multiply by doubling, that us a HUGE head start over simple water column seeding. Bacterial proliferation occurs on a log scale whereas purification occurs linearly. So if I transfer 1000 bugs over in the water column to one tank and a million over to another one by seeding of some other sort, then the later tank will always have a million fold more bacteria than the other, assuming that they multiple at the same rate, and only until the later hits the limit of supportable bacteria.

 

[mfdrookie516]

Someone made the comment that scientific experiments weren't necessary.. but IMO, to get a definitive answer on most of the questions brought up, they are. One can only speculate that most bacteria live in the filter in the majority of tanks. I can tell you that I've got two tanks running with no filter media. One is lightly stocked with only a bristlenose and 4 otos (29g). The other is a 150g that's pretty heavily stocked. Both are planted. Both only have mechanical filtration that's replaced (not rinsed) every week or two. I've yet to detect any ammonia or nitrite, and very very little nitrate in either tank. This leads me to the suggestion that bacteria will make themselves a home wherever necessary... I don't know all the science behind the various types of bacteria, whether they are free swimming or not, etc etc... I do know that what I've done has worked for me (for 4 months now... not a big acheivement, but promising.

FWIW, I did it as a test and it worked. I tried on a smaller scale first, and it worked.

 

[aqua_chem]

I also don't think that space is a huge issue actually. Most bacteria can attach to other bacteria and form colonies. So when they don't have enough room to grow out anymore, they would probably simply grow up. I would think that they would hit a nutritional barrier long before they hit a spacial one.