open or closed?

[gregt]

Here's a good ponderance.

Are our reef tanks open or closed systems?

[tankgirl2]

my vote; Open - because we can export nutrients and inorganics (via skimmer, charcoal, siphoning, etc.) And, open at the other end because we can add stuff.

[mojoreef]

Well technically they are open, but your really grasping at straws when you relate it to a truely open system. By saying closed systems we are trying to shin a light that we cannot recreate the ammount of flow, water mass, filtration, bioload and so on. So its open but still a crummy representation.


mike

[jwwill0]

Arguments could be made many ways depending on the system boundaries. Here's a couple:

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With the boundaries defined as the aquarium itself, and connecting systems (i.e. sumps, fuge, etc.):

Technically open, with extreme limitations. The fact that water evaporates and is replenished with fresh, and we (sometimes) do water changes, export nutrients, or generally add or remove anything makes it an open system. HOWEVER, it is actually more like a semi-batch process. The system is open, but not continuously. In a truly open system, like the ocean, mass transfer occurs among the nutrients in the water allowing it to maintain a somewhat stable Net Zero effect (i.e. you might find a pocket of water with a higher concentration of calcium than another, but that calcium is free to migrate to the areas of lower calcium concentrations over time). In our systems, however large your tank is, the concentration of things such as nitrate or phosphate can continue to build up, with no where to go unless steps are taken to change the system ecology. This buildup, then subsequent reduction takes place on an entirely different scale and rate than in a system that can act continuously, making it more batch-like.

The ocean interacts with the entire world. My aquarium only interacts with what I want it to, when I want it to, if I want it to, good, bad, or otherwise. The only thing that happens between my tank and the world around it without me being involved is evaporation, which could also be stopped. Try stopping evaporation from the ocean.

*********************************

Another entirely different way of looking at this is to say that the aquarium is open and the ocean is actually closed. The ocean's system boundary would be defined as the entire world, and transfer in and out of the ocean, and within, are all contained within the system.

My $0.02

[Spanky]

Using the correct terminology as used in marine biology.

Open system - Open to running sea water.

Closed system - Not open to running sea water.

That has a slightly different definition when used by marine ecologists.

Open system - populations maintained by recruitment from many locations.

Closed system - populations maintained solely by local recruitment.

I know where you're coming from on this Greg and that's just one of many things that he should know and doesn't.

[gregt]

I know where you're coming from on this Greg and that's just one of many things that he should know and doesn't.

Well, that's what brought it up, but I think it's a good "thinker".

[gregt]

Here's my take:

It depends. The terms open system and closed system have always been (to me) confusing and misleading all at the same time.

It's really relative to how you are studying the system and what you consider imports and exports.

I suspect that you would be hard pressed finding a truly closed system in real life. It's a matter of scale. A system may be relatively closed, but I'm not certain how you can really define any system as being closed.

There's always going to be an effect from some other system in some tiny way or another.

Now for my opinion on reef tanks. I have always consider our tanks to be "closed" systems. I feel this way mostly due to the fact that a huge amount of the system can not move out of the system on a regular basis. Water changes just aren't enough for me to consider a system "open". Inputs of light, and exports of heat and a tiny amount of gasses, just don't add up to enough when the sum of the system is considered.

So, technically, I think all systems are semi-open, but in practical terms, I believe that our tanks are very much closed.

My 2 cents.

[jwwill0]

Originally posted by Spanky
Using the correct terminology as used in marine biology.

Open system - Open to running sea water.

Closed system - Not open to running sea water.

That has a slightly different definition when used by marine ecologists.

Open system - populations maintained by recruitment from many locations.

Closed system - populations maintained solely by local recruitment.

I know where you're coming from on this Greg and that's just one of many things that he should know and doesn't.

Ok, if I understand correctly, by both definitions above, the reef tank is closed, and the answer to Greg's question is fairly cut and dry.

Since the original question didn't specify a definition of open or closed, I used my "chemical engineering" view. A system is closed or open based on the assigned boundaries. In this case the assigned boundaries are the definitions of either marine biology or marine ecology. Is this right?

[SPC]

Originally posted by gregt
Here's my take:

It depends. The terms open system and closed system have always been (to me) confusing and misleading all at the same time.

It's really relative to how you are studying the system and what you consider imports and exports.

I suspect that you would be hard pressed finding a truly closed system in real life. It's a matter of scale. A system may be relatively closed, but I'm not certain how you can really define any system as being closed.

There's always going to be an effect from some other system in some tiny way or another.

Now for my opinion on reef tanks. I have always consider our tanks to be "closed" systems. I feel this way mostly due to the fact that a huge amount of the system can not move out of the system on a regular basis. Water changes just aren't enough for me to consider a system "open". Inputs of light, and exports of heat and a tiny amount of gasses, just don't add up to enough when the sum of the system is considered.

So, technically, I think all systems are semi-open, but in practical terms, I believe that our tanks are very much closed.

My 2 cents.

This is the way I have always looked at it too.

I think the Doc brought up the point he did simply to try and discredit someone. It didn't work IMO, I would bet that 99% of hobbyist see our tanks as closed systems, just like an ant farm
Steve

[Awestralian]

Define open or closed as posed in this question.

The world is closed, so that would make all the natural reefs closed systems?
Because i dont see much difference in natural reefs and tanks as far as importing and exporting go, only that we (humans) do the work on our tanks, where as nature takes care of it on natural reefs.

I would say our tanks are open, for much the same reasons as tankgirl2...

[wizardgus]

Sorry...I gotta.

IMO semantics are a great bulwark to hide behind when losing an argument or the facts elude you.

Back to college days..."If at first you would debate me, define your terms."

I think we do an admirable job of trying to make our tanks an open system or replication of an open system. I think the tanks of old were most certainly closed systems. And if scale is considered, despite our best efforts our tanks are yet today.

As much as the coral curmudgeon can tic me off some times, I always liked Eric B's analogy, "If we are going for scale, then a tank the size of an olympic swimming pool, with one coral colony in it, would be grossly over-stocked."

Well, I feel better.

[Awestralian]

Back to college days..."If at first you would debate me, define your terms."

[Geoff]

i do not think you can get anymore closed than this.

Ecosphere

G~

[Awestralian]

Originally posted by Geoff
i do not think you can get anymore closed than this.

Ecosphere

G~

LOL!
Those look cool!

[gregt]

Sure you can. Wrap it in 20 feet of insulation to prevent light from getting in and heat from getting out.... But it'll still not be completely closed. There will still be electromagnetic radiation, radio waves, etc......