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My 29 gal planted tank has been running for several years. I had about 2 wpg on it for a while and had some more exotic plants, but they got killed by cichlids, and now I've gone down to a basic low-tech planted tank.

All that's in the tank is three inches of pea gravel (kept moving my MTS), driftwood, one black-neon tetra, one firemouth (cichlid), a crypt wendtii, a half-dead aponogeton, some java moss, and some rockwork (and water, of course)...

Before I go off on my plan of what I'm going to do to this tank, you'll need some background info. You all know how the nitrogen cycle works in FW, right? Ammonia -> nitrite -> nitrate. Both of the conversions are done by bacteria. In saltwater, the nitrogen cycle is completed by another species of bacteria that consumes the nitrate and releases nitrogen gas (in the form of bubbles) into the water column, and into the air. Most people don't know this, but there IS a species of freshwater bacteria that does this as well, but it's so exotic that nobody has really tried to culture it in a freshwater aquarium. A few years ago, I did a whole bunch of research on this bacteria (Paracoccus denitrificans) and was able to obtain a culture from a local source. This bacteria requires almost completely stagnant water to live in, and a constant source of carbon... they usually live in the sludge in the bottom of lakes and ponds... something you do NOT want in your tank, right? Wrong!

"Denitrification is the reduction of nitrate to nitrite and then to nitrous oxide or nitrogen gas. Denitrification is normally performed under anoxic conditions, which is comparable to anaerobic conditions except for the presence of nitrate and/or nitrite. In natural or aquaculture ponds and lakes, this condition is found only in the sludge, but in wastewater, the condition can be created by adding nitrate to collection systems, anaerobic lagoons etc., or is created by addition of wastewater that formerly contained ammonia, following nitrification..."
-http://www.alken-murray.com/BioInfo2-03.htm

Basically, I built a reverse-cannister filter with a tiny pump, CRAMMED it full of media (two different types of filter floss, three types of sponges, ceramic rings, and some other random stuff) and carbon, introduced the strain of bacteria to its new home, sealed the filter, and let it run. After a few months, my nitrates dropped to 0ppm. I re-tested with a different test kit to confirm the results (it also tested at 0ppm). Horrendous amounts of cyanobacteria began to infest the tank shortly after my nitrates bottomed out (as they thrive in nitrate-free environments), but I just turned over whatever it grew on and it died and then re-grew on top, and then I turned it again, etc. Eventually, I took most of the lights off of the tank (down to 20w 10,000k over 29 gal), lost most of the fish due to them killing eachother, and I ended up with a firemouth and a black-neon tetra that's left.

I've got massive colonies of protist organisms thriving in the tank--living on plants, in the substrate, etc. The fish feed off of these protists and off of the few plants that are left, so I never have to feed the fish anything. Yes, I do keep an eye on them, and I do have food that I can feed them if they look hungry (if their belly is concave, that is)... but they're always relatively plump from eating so much, so I never feed them.

I usually do waterchanges in the tank once or twice a year. I'd do them more frequently, but there isn't any reason to. The fish and plants are happy and healthy, parameters are always perfect, and the substrate is kept moving by MTS. The only reason I really DO waterchanges is because I get paranoid and do it 'just in case' something were to go wrong, which has never happened.

All I've done to the tank in the last 8 months is top it off with fresh dechlorinated water once or twice a week. I haven't had to do anything else--no cleaning, no waterchanges, no adjustments to the filter or heater... nothing.

There are plants in the tank that photosynthesize, and I think that the simple fact that there are WAY more plants in the tank than fish, that if I totally seal off the tank, the plants would be able to keep up with the oxygen demands of the fish.

So here's the plan: I've got a couple big sheets of glass that I want to cut down to size so they'll cover the top of the tank. I'll have to construct some sort of self-cleaning internal filter mechanism so I can take the HOB off of the back of the tank. I'll cut a small corner off of the sheet of glass so I can run cords for the heater and filter and tubing for the reverse-cannister filter/bacterial refuge. I'll leave it like that for a month to make sure everything is going alright. If everything goes as planned, I'll silicone the glass to the top of the tank and seal the system off from the rest of the world!

Environmental scientists would call this a complete 'closed system'. No matter can go in or out of the system--only energy in the form of heat, light, and radiation will enter or leave the system. In theory it will be self-sustaining, but only time will tell.

All chemical cycles will be completed in the system (that's the only way it'd be able to work, of course)--water, carbon, nitrogen, etc. The fish do munch on the plants, and they do return nutrients back to the water column for the plants to re-absorb.

Here are the only problems I can think of with this experiment:
- I'll be unable to monitor any parameters other than temperature. I've seen little 'ammonia detector' things that stick on the inside of the tank, but I don't know how well those work. I may look into getting one of those, and I'll see if they make them for monitoring other parameters.
- Some parameter may go out of whack and I won't be able to do much about it other than ruin the experiment by breaking the seal on the tank (the one month trial period should lessen the chance of this happening, but you never know)
- I may lose livestock--fish, plants, bacteria...
- pressure created by heating and cooling of the tank may cause problems... I'm going to have to keep the temperature as stable as possible.

What are your thoughts on this? Am I missing anything? Can you think of anything else that may go wrong that I could potentially fix before it does go wrong? Do you guys have any suggestions for this project? Do you have any ideas on how to monitor the water parameters?

I'm totally open to suggestions... I'd love some feedback before I do anything with this.

Thanks in advance!

Edit: They DO make stick-on tests for pH and ammonia, but they're supposed to be replaced every 4-6 weeks 'for best results'...

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Hi,
When you break it all down, you are trying to recreate a
"Perpetual Motion" system. I believe the laws of physics
argue strongly against its existence.

I do think that your efforts are worth a paper or two and
that you might present them to a couple of authors to see
if your results can be duplicated. I've heard of others
attempting this as well, but I don't recall any really
successfully results.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

It's not exactly perpetual motion, per se, because energy does flow through the system. Both light and heat are let into the system--that is part of the definition of a closed system.

With a theoretical perpetual motion machine, friction and air resistance (unless it's in a vacuum) eventually stop the movement. In this scenario, nothing is being stopped... just recycled.

Earth, as it stands today, is almost a closed system. Very little goes in or out--just satellites and meteorites. As you can see, Earth has maintained itself very well throughout the last billion or so years that life has existed here. This tank is the same idea... just on a MUCH smaller scale...

I've seen these little glass bubbles that you can buy that have a single little shrimp and a rock in them. You put it in the sun, algae grows on it, the shrimp eats the algae, the shrimp excretes waste, the algae feeds on the waste and grows, the shrimp eats the algae again, etc. The algae also provides the oxygen for the shrimp, and the shrimp provides CO2 for the algae. What I'm trying to create is something similar, but on a larger scale than that, with many more organisms involved.

That said, I think that it may be possible for this experiment to succeed, but it may be quite a challenge--a challenge that I very much look forward to.

The one thing that I love about this hobby is that it is so incredibly limitless. You can really take it as far as you want to. Tanks--both incredibly small and incredibly large--can be set up for very specific or generic purposes. I've seen tanks ranging from 0.4 gallons (no fish obviously, but corals) to 1.4 million gallons. Yes, things may lose their novelty, but there's always something else to do. For example, tanks I have planned include a 3.7 gallon non-photosynthetic/blacklight reef (for tubestrea, gorgonians, etc), a 0.4 gallon SPS reef complete with a skimmer and sump, a 10 gallon tidepool tank (haven't decided if it's going to be brackish or full SW yet), and several others. Sure, you can always keep a tank full of tetras, but that gets old. There are always new and exiting challenges to take on and either fail or succeed with. No matter how far you get into this hobby, you can still learn more every day.

Anyway, I'm done rambling...

Let me know if you've got any other ideas/suggestions/questions/comments for the sealed tank

Thanks

well i reckon it sounds cool mate! good luck to you.
i had a friend when i was living in spain and she was thinking of going into business selling enclosed systems which had tiny shrimp (i think) and some sort of plant in an enclosed glass container. it looked very cool and was to be sold as a live ornament. anyway she left hers to near the radiator and every thing died! i think she abandoned the idea after that.

sorry dont that was not ment to have any reference to your project its totally different and just something that your idea reminded me of!

as i say good luck with it sounds very cool. imagine that as a job? installing huge self contained habitats! would be awesome!

sounds cool, but what happens when your heater malfunctions??
For this reason i would use an in cannister heater

I feel it would be best to remove the larger livestock.However well it may work for a month, it will go south quickly with a rotting firemouth carcass.

Set a one way, tap valve and tubing, attached to a syringe into your water for the purposes of monitoring should the need arise. Water removed could not be replaced, but if it is a choice between that and opening the system the loss of some water would be the better choice. The valve would prevent anything being added.

You will also need a pressure valve somewhere that will blow should it come to that. Exploding rotting tank doesn't sound fun.

For a month, my bet is that it'll work. Heck, you can keep a guppy alive in a sealed coke bottle with a bit of elodea for a few days. Longer term, I'm not sure that it has the qualities of something that is sustainable. For a start, there is a history of death and dying, and although that is natural, by the sounds of it there is more dying than living, and very little reproducing.
The ratio of air to water is likely to be out, so that is a bit worrying. For the depth that known life goes into the earth's crust, there is an awful lot of sky above it. My bet is that the concept for this setup is primarily water based.
The plants would not only have to cater for the oxygen demands of the fish, but of the bacteria, the microscopic bugs, and themselves, which is a mighty task for a crypt, a half-dead apon and some java moss. Were you going to add more? all submersed?

It is an interesting idea, but on such a small scale and such a specific chunk of environment, I'm not sure if it'll work.

There was discussion on this about 4 years ago. Apparently there is a large dome thing somewhere in the UK which is pretty close to a closed system. I can't recall what it is called, but it might be worth looking into.

For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. - Terry Pratchett

Thanks for the input, folks!

I forgot to put in my last post that this is an experiment... it is NOT something that I'm going to continue if something goes horridly wrong and I decide that it just won't work. If the firemouth (3" right now... just a li'l guy) does, I'll obviously have to remove the carcass, maybe replace it with a smaller fish, and I may re-start the experiment.

Fandan, that is what I was talking about... a little glass bubble with a shrimp and algae. I saw them online a while back. At least it was something similar...

Desiredusername, if the heater malfunctions, my room is 75-80F all the time anyway (I blame my server and my reef tank!), so everything would probably be fine (unless, of course, the heater got stuck ON... which AFAIK only Tronic's are known to do, and I have a Visitherm)...

Calla, I think I'm going to drill a 3" hole on each end of the top glass and put a ball valve on each one. That way, if something goes wrong, I'll be able to open them both and put a fan on one of them and put an airstone in the other or something to get O2 up. I'll also be able to fit my hand through a 3" ball valve.

I'll definitely look into installing some sort of pressure valve, where it would release as soon as a certain PSI was reached. I'll have to set up some sort of monitoring device or mechanism so I'll be able to know if it has had to release (thus ruining the experiment). A failed experiment would be far better than an exploded tank.

Maybe I could set up some sort of sealed-off glove so I'd be able to reach in and move things around, but nothing would go in or out of the tank. You know, something like what you see in sci-fi movies that they use for handling hazardous materials in the lab... the big box with the two big gloves that let you reach into the box. Know what I'm talking about?

Also, Calla, I am going to drop the water level about 4" and have some pothos grow emmersed. I'll probably end up with a few more plants in the tank as well... I'm not sure what yet, though...

I've got fish club meeting in a few weeks where I'll ask everyone for their ideas/suggestions, and I'll see if I can borrow a glass drill bit for the holes.

I'll probably end up writing a paper on this experiment... maybe I could get it published somewhere... maybe Adam would want to use it as an article here on FP?

Thank you all for the comments and suggestions... I appreciate it! Keep 'em coming