Hypothetical Question

[Cliff]

Could you.... Yes

Should you.... No


I can go to a fast food restaurant and for the next 2 or 3 years eat nothing but greasy burgers and frys morning noon and night. I would still look and act healthy, right up until the time I developed health problems from improper diet.

An argument can be made that my analogy might be a little on the dramatic side, but my point remains the same.

You can be lucky for quite some time, but at some point you will have to pay the piper

[talldutchie]

Could you.... Yes

Should you.... No


I can go to a fast food restaurant and for the next 2 or 3 years eat nothing but greasy burgers and frys morning noon and night. I would still look and act healthy, right up until the time I developed health problems from improper diet.

Going to be a lot sooner than 2 years Cliff. ;-)

I still think setting up a shrimp bowl is a good idea for anyone interested in learning how plants actually interact in an eco system.

[Indian Woods Angels]

I am going with yes. The system would have to remain absolutely closed and tightly contained. There could be no intervention. You could not add anything into the system nor take anything out. Evaporation could not be allowed to occur. Within this system all things would eventually find balance, could this system satisfy visually our expectations of a successful keeping of an aquarium ? Possibly not. Could this system find it's own balance and find a way to sustain itself on those items closed within itself, yes. Even through what might be perceived as a crash or a catastrophe we would have to have patience and let the system show us it's next phase. Even if it consumed all of it's vital elements and placed them into vegetation or into substrate we would have to see what the cycle shows us and be patient towards how the system would balance. Our natural world has many habitats that we would consider to completely crash each year in a seasonal shift. These places look so remote or so far gone that they magically transform back into bloom.

A better question might be: Could we be patient enough to allow for the existence of a closed system?

[Sandz]

I would maintain that for the benefit of the floura and fauna of the tank that you continue waterchanges if you are an aquarist. We could swim in a pool filled with urine, and some would evaporate, if we topped it off with urine it would become more condensed and so on and so forth. Same with the fishes excrements. Even with propper planting, not everything is churned over. There are discus tanks that do 1 a month of 25% who maintain reffugiums to remove nitrates. Such tanks can be sustained but even by said owners it doesnt allow for "optimal" conditions.

You could go years without changing the water in your tanks and continuously add the topoff amnt. Without actual maintenence, you will find less than optimal conditions on a depleting scale.

[Cermet]

Impossible without an algae scrubber - the nitrates will build up and become toxic; it would take a high ratio of plants to fish to allow 'a closed system' to work. Minerals as some have pointed out would need to be added.

[myofibroblast]

Listening to a podcast a listener asked a hypothetical question.

"If a home aquarium is large enough, bioload low enough, and filtering is strong enough, would it be possible to operate a aquarium without completing water changes?"

The question itself presents several a priori problems:
1. What is the purpose of a mechanical filter in a closed system?
2. Are you assuming no addition of elements to the system (including oxygen, carbon)?
3. Are you assuming no energy transfer (e.g. from heat dissipation, heat absorbed through the electrically powered mechanical filter)?
4. Related to #2, you would have to assume a natural food chain is established in that closed ecosystem such that the fish will find the food they need within the system, otherwise you're adding elements (nitrogen, carbon, etc) to your system and it, thus, cannot be considered a closed system. It would be a system of increasing nitrogen and carbon source, in whatever elemental form they may be. In that case, the question is non-sequitur.

I speculate that an equilibrium will be established eventually in a perfectly closed system. That equilibrium, however, will very likely not contain live fish as we know it. As the dead fish decompose and become part of the nitrogen and carbon cycle, I'm sure a new balance of much smaller and/or simpler life forms (like single celled organisms) will emerge.

[coarb34]

nature itself does provide an answer with dams that only get rain water to replenish the water, so why not something smaller enough. A better question is how much money would such a system cost to build, would it run of electricity and how much would you are you willing to spend on construction. My answer is yes. Properly researched and built with only rain water to top up the tank and if you had a big enough piece of land to do it. Science and technology is already years ahead of what we can comprehend all ready, we have more information at our fingertips than our parents.

just look at our hobby itself how far it has progressed in a hundred years