self sufficient aquarium

I'm interested in creating a completely closed ecosystem, with an airtight sealed lid. Is this possible? All the tanks alike I can find are not sealed to allow human meddling from time to time. My main question as of now is, what plants grow fast enough, and secondly would I need a predatory fish to keep the herbivorous fish in check? I really don't know anything about the subject if anyone has any info or literature recommendations.

I'm interested in creating a completely closed ecosystem, with an airtight sealed lid. Is this possible? All the tanks alike I can find are not sealed to allow human meddling from time to time. My main question as of now is, what plants grow fast enough, and secondly would I need a predatory fish to keep the herbivorous fish in check? I really don't know anything about the subject if anyone has any info or literature recommendations.

Well, the idea of it being air tight doesn't seem beneficial. While I know little about the mechanics, I have a hunch that the having water surface exposed to open air is helpful for gas exchange. I think your plants/fish may suffer as the air inside may, for lack of a better term, grow 'stale'. Maybe others can expound upon this idea.

Josh H

I highly recommend the book Ecology of the Planted Aquarium by Diana Walstad. A lot of the answers you seek are in there.

Years ago they sold these things called "Eco-Spheres". They were little balls that had water, algae, and a few shimp. While the shrimp lasted a while, they supposedly just slowly starved to death.

In nature, there is a huge volume of water for each fish. If you can devote a huge tank, it might be possible I suppose, but I think it would be very difficult to get the balance of light, volume, etc. correct.

I highly recommend the book Ecology of the Planted Aquarium by Diana Walstad. A lot of the answers you seek are in there.

While Diana's book is nice and a great introduction to soil-based tanks, some of the science is speculatory and based on few observations (she does admit this, but it seems that some people take her observations as gospel instead of as anecdotally).

A good college-level aquatic ecology book might be more what you are looking for.

While Diana's book is nice and a great introduction to soil-based tanks, some of the science is speculatory and based on few observations (she does admit this, but it seems that some people take her observations as gospel instead of as anecdotally).

A good college-level aquatic ecology book might be more what you are looking for.

More books! I just spent $125 at the convention! This is true though, though prior to burning more money I'll speak with one of my ecologist friends.

My first thought was also that the fish to water volume ratio was massive in nature, but that is also true for plants. If I had a really densely populated(with plants) tank do you think the plants could sustain it at a reasonable size? I don't want to go over 125(I'd hate to crush my neighbors downstairs.) which could be the final nail in the coffin of this. Maybe after grad-school I can up-size.

My first thought was also that the fish to water volume ratio was massive in nature, but that is also true for plants. If I had a really densely populated(with plants) tank do you think the plants could sustain it at a reasonable size? I don't want to go over 125(I'd hate to crush my neighbors downstairs.) which could be the final nail in the coffin of this. Maybe after grad-school I can up-size.

My 55 gallon tank isn't too large, and it works pretty well. I feed my fish flakes, and I have nice bright, full spectrum lights and well nourished substrate (kitty litter) for the plants to grow in. The ammonia and nitrite stay at 0 ppm and the nitrate in the past was very low (0 to 15 ppm), but I have stopped measuring it. I harvest the plants every now and then and sell them to other aquarists. And that's about it. No water changes, no gravel siphoning (no gravel to siphon, anyway). No disease flare ups or unhealthy fish. It's really very nice.

Picture of my 55 gallon aquarium: http://gallery.nanfa...n tank.jpg.html

As to whether or not the science in Diana Walstad's book is based on few observations, well, you can be the judge of that yourself. She lists all of her sources at the end of every chapter, and you're free to read those sources yourself. The reason why I like her book isn't because I agree with her on everything (I don't) but because there are a lot of data and graphs presented from peer reviewed studies. The information is all there, and if you use your own mind to analyze it and find you come to the same conclusions that she does, well, that's great. If you yourself look at that data and think, "That doesn't does not support Walstad's conclusion" well, then that's also great. You're going to have to look at it yourself and see what you think.

Also, it's not an expensive read. You can buy the ebook here for $13: http://www.diesel-eb...Aquarium/1.html or can rent it from your local library. I personally own a copy, because it's not the sort of book you can read in one sitting (anyone who's ever tried to read straight through a textbook will know what I mean).

I read a Discover article once saying that despite major losses (such as the die off of corals due to acidity when it was used to test CO2 levels) the fish in Biosphere 2's aquatic habitat are thriving with no one feeding them.

A few years ago I set up a 5gal aquarium in a sunny window. I put a thin layer of soil under the gravel, made a cute little aquascape with some river bricks and a broken terracotta pot. I planted it with Lilaeopsis brasiliensis, Hydrocleys nymphoides, and some Spirodela. Once the chemistry had settled for a week or two I tossed in a few cups of local pond water to get some microfauna going. A few weeks after that I added a couple Heterandria formosa, put on a screen top, and left it. When the water level would drop a few inches I'd add more (I had awesome tap water at the time, so no mineral buildup), but topping off the water was the only addition I made. I never once added food to the tank and they lived about 2-2.5 years, picking at the little pond micro-critters in there. I would test the chemistry now and again and it was always well within safe limits. It was one of my favorite aquariums ever. Not totally sealed like you are looking for, but it's a step in that direction.

I have set up several mostly self sufficient tanks. I.e., tanks that needed nothing but water top-offs.
They were, more or less, a "Walstad" style tank.
Flagfish and sailfin mollies, (and other poecilia) seem to work well as residents.
The last one set up was 33 gallons.

Contents:
Fish stocked-
5 fff (1 male, 4 female), 3 leftover wild poecilia latipinna fry.

Inverts-
Lumbriculus variegatus (blackworms), tubifex worms, unknown sp. pond snails, two species of ramshorn snails (common and 2-ridge), 5 or 6 grass shrimp. Plus whatever was in the old, still wet, ecocomplete (planaria for sure).

Plants-
Hygrophila difformis, duckweed, hydrocotyle ranunculoides, some random anubias.

Substrate layers-
Handful of peat, 2" garden soil, handful of osmocote, 2" old ecocomplete.

Hardscape-
Medium sized piece of bogwood, couple big chunks of red chert.

Lighting (possibly a little controversial)-
110w (55w x2) of 5500k, suspended about a 14" above the open top tank. 10 hours a day.

Tank temp-
70-76f, unheated.

Pumps/equipment/other-
One small powerhead with a 3"x3" block of coarse filter foam over the intake (to keep sails and fry out).

I figured the extra light would really drive the floating plants (duckweed, hydrocotyle ranunculoides), while still providing enough light through the floaters down to the other plants. The fff and mollies are omnivorous but can be primarily vegetarian. Plus, the open top and light drew in occasional bugs that made it indoors.

I had the tank up and running for about two months without the fish. The duckweed started taking over, and I added the fff's and mollies as duckweed grazers, which they did very well. There was also some green string algae (not as much as you'd think with the very high light) which vanished within a few days. I checked the ph once over the run of the tank, at about two years old, and it was mildly acidic (6.7 or 6.8, iirc). The "hardwater" mollies didn't seem to mind.

After adding the fish, I added nothing but water for several years. Though I did cull extra fff and mollies as they were born, and when I needed them in other tanks.

Other than adding water, I'd call that tank self-sufficient.

I've got a 6 or 7 year old half whiskey barrel/pond in the greenhouse that has a bunch of stuff in it- hydrocotyle ranunculoides, a couple gambusia, scuds, blackworms, 6" of dirt, a lot of bugs...

Rick

It's hard to get one of these to last any amount of time with small invertebrates and algae. With fish and vascular plants, I would be willing to bet you're just making a large sealed box of dead stuff. Without the lid on top it's definitely possible, but sealing it just introduces a huge complication.

If you're set on doing this, I'd try to find a very small herbivorous fish to put in. You want to keep the system fairly low in biomass. It would be very unlikely that anything you put in there breeds, and a predatory fish would just clean the place out in a day. For a stable population of herbivorous and predatory fish, you need a very large body of water.

Edited by jasonpatterson, 25 June 2011 - 09:51 PM.

One thing to keep in mind that plants don't undergo photosynthesis in the dark but do continue to respire, so if you pack the aquarium with too many plants you could suffocate your fish if left in the dark too long.
Also, although I'm sure your expectations weren't that such an aquarium would last forever, another thing to consider is that not everything produced in the aquarium is going to be able to be used by something in the aquarium. That is, when a fish eats a portion of a plant some of that mass gets incorporated into the fish some becomes waste. The remaining plants will be able to use some components of that waste to grow more plant material, but not all of it. There will be bacteria, fungi, etc... that will be able to use some of those remaining components and may even convert them into components that the plants can use, but there will always be something left that nothing in your aquarium will be able to use. The same thing will be true of dead plants and fish. Thus over time the available nutrients are going to diminish and throw things out of balance even if you are able to find that perfect balance to start with. Of course the larger the aquarium, the longer this would take.

One thing to keep in mind that plants don't undergo photosynthesis in the dark but do continue to respire, so if you pack the aquarium with too many plants you could suffocate your fish if left in the dark too long.
There will be bacteria, fungi, etc... that will be able to use some of those remaining components and may even convert them into components that the plants can use, but there will always be something left that nothing in your aquarium will be able to use. The same thing will be true of dead plants and fish. Thus over time the available nutrients are going to diminish and throw things out of balance even if you are able to find that perfect balance to start with.

Diana Walstad estimates the nutrients required for maintaining plant growth in her book, where she does what we chemical engineers call a mass balance. With her setup, totaling what goes in and out and what's in the substrate, she estimates that she only needs 2 ppm nitrate to keep the plants well fed. All the math is right there.
Also, the humic substances produced by the plants over time (those 'wastes' you're referring to) are actually really beneficial to fish. They bind to heavy metals in the water, reducing their toxicity by reducing their ability to be absorbed by the fish.

One thing to keep in mind that plants don't undergo photosynthesis in the dark but do continue to respire, so if you pack the aquarium with too many plants you could suffocate your fish if left in the dark too long.
Also, although I'm sure your expectations weren't that such an aquarium would last forever, another thing to consider is that not everything produced in the aquarium is going to be able to be used by something in the aquarium. That is, when a fish eats a portion of a plant some of that mass gets incorporated into the fish some becomes waste. The remaining plants will be able to use some components of that waste to grow more plant material, but not all of it. There will be bacteria, fungi, etc... that will be able to use some of those remaining components and may even convert them into components that the plants can use, but there will always be something left that nothing in your aquarium will be able to use. The same thing will be true of dead plants and fish. Thus over time the available nutrients are going to diminish and throw things out of balance even if you are able to find that perfect balance to start with. Of course the larger the aquarium, the longer this would take.

Not forever? You obviously do not know me! No, this would be a project that would take many years on my part and then it may not be possible, but I believe organisms adapt to their environment even if it's not perfect so I think it is possible. I want this to be sitting on my grand kid's mantle. I'll have to do more research, it would certainly make a good paper.

Most of the replies to this seem to be leaning toward standard tanks that require minimal care. Setting up a tank that requires minimal care is very easy. Getting it to survive long term is a little harder, but it's still no great feat. Removing the atmosphere is a massive change.

Some thoughts about a few of the difficulties sealing it will introduce:
You're probably not going to have any circulation in the system beyond the minimal amount that convection provides. There are some (very expensive) cordless pumps, but if you're serious about trying to put together a system that will last a century, the pump will fail at some point and you'll lose your circulation. Probably best to design it without a pump to begin with. That's going to mean that any gas volume you leave in the tank, or that will inevitably form as a result of the action of bacteria in the system is going to have fairly poor interaction with the water, especially once it gets that nasty oily coating on it.

If you don't include any sort of air pocket, I'm guessing that the system will pressurize. There will inevitably be a bubble or two in the system. Since the container you're considering is more or less constant volume, any gases that can't dissolve in the solution will pressurize that bubble. Pressurizing the bubble (no matter how small that bubble is) means pressurizing the tank as well, and it will leak as a result. It would probably be a good idea to include a sizeable volume of air (or perhaps oxygen) in the original setup to try to avoid this, as a larger volume would experience much smaller pressure swings from addition/subtraction of gases as the temperature changed and the chemistry of the tank altered (day and night, for instance.)

Substrate could be a challenge. Most plants are going to need some sort of substrate that provides nutrients and ion exchange. Unfortunately (or maybe fortunately?) these types of substrates often are going to decompose to some extent over time. Things like hydrogen sulfide, which are stinky but not a huge deal in reasonable quantities in a standard tank, are going to be stuck in this system and dissolve in the water.

You might consider trying this on a small scale with a 10g aquarium and some algae/invertebrates. I've had systems of this type last perhaps 18 months before the macroorganisms died off. Algae and microorganisms last much much much longer, of course, but that's not a lot of fun to look at with the naked eye.

ETA:
One additional thought. If you weren't just being sarcastic about the thing lasting for a very very long time, consider the weight of the system and the extreme difficulty in moving it. A filled 125g aquarium weighs 1400lbs, and you wouldn't be able to drain the water when you move around.

Edited by jasonpatterson, 26 June 2011 - 03:51 PM.

I'm interested in creating a completely closed ecosystem, with an airtight sealed lid. Is this possible? All the tanks alike I can find are not sealed to allow human meddling from time to time. My main question as of now is, what plants grow fast enough, and secondly would I need a predatory fish to keep the herbivorous fish in check? I really don't know anything about the subject if anyone has any info or literature recommendations.

If you are crowd-sourcing this for NASA's Humans-to-Mars project, there really should be a prize. A big one.

Otherwise, why go out of your way to make things really, really difficult? Some degree of "meddling" is necessary because understanding, constructing and initializing a micro-environment that can continue indefinitely in a sufficiently stable fashion is beyond our current knowledge and abilities. (In a sense, meddling is a cost-effective way of compensating for the inevitable deficiencies of the original design. Which is not to say that all meddling interventions will be successful, of course.)

Unless your "completely closed ecosystem" includes a small sun as a source of light energy, it's not really closed and self-contained. Like all other aquariums, it'd be a grossly simplified subset of the complexity of an actual native ecosystem, which would or would not "act naturally," depending on what specific dimension/s you're looking at.

So if you just want to enjoy fish in an environment comfortable to them, go low-maintenance. But if you thrill to a bio-engineering challenge, that's okay too, we have all kinds of odd-balls in our community and hobby. (All the present company, pointedly included.)

The challenge is to tinker with the second law of thermodynamics, which will drag you down with entropy and loss in general.

Not forever? You obviously do not know me! No, this would be a project that would take many years on my part and then it may not be possible, but I believe organisms adapt to their environment even if it's not perfect so I think it is possible.

(Since I still believe in evolution, this is a minority opinion.)

In the LONG RUN, organisms do adapt to their environment. Lots of examples from the aquarium literature (esp. killifish) of "aquarium strains" that have diverged from their ancestral stock in 20 to 50 generations, at least in terms of color patterns, which is what we lay-people can most easily detect. This could be survival-of-the-fittest at the micro level, but is much more likely (IMO) to be random bottle-neck effects due to very small populations and sparse genetic pools.

But in the SHORT RUN, individual organisms make do with the flexibility they're infused with via their genetic inheritance ... OR they become extirpated in their local environment.

A small self-contained environment may have some adaptation taking place over a period of many generations. But what is more likely is that most of the sub-optimal creatures become extirpated, so what is left is the subset of creatures that were pre-adapted to thrive in the conditions we have created for them.

The challenge is to tinker with the second law of thermodynamics, which will drag you down with entropy and loss in general.

Depends on how much energy is put into offsetting the entropy. Entropy is inevitable but can be held off. Can you do what nature does and have the base energy input being the sun thus letting the plants and animals handle it themselves?

I wonder what the ideal tank size is for having a self supporting producer, primary consumer, secondary consumer food chain.

You can do something pretty close to self-supporting with microbial communities, in what are called Winogradsky columns. Those organisms are more forgiving of suboptimal energy flows, certainly compared to multicellular plants and animals.