Vacuum suspended fishtank: Why would this design work or not?

[gazaah]

TL;DR Summary

I am designing a vacuum suspended fish tank. But I don't know enough to understand whether the design on the right would work as well as the design on the left.
I don't want a big open area of water, I want a few inches at the bottom for aeration and access to the pump and plant roots.

It am looking at a larger volume, about 75 gal/280 liters.

I know people have used vacuums to do crazy things, such as to have many thousands of gallons with little portholes to pet the fish.

 

[russ_watters]

Summary: I am designing a vacuum suspended fish tank. But I don't know enough to understand whether the design on the right would work as well as the design on the left.

Yes, from a physics/engineering point of view it will work. My concern would be how to successfully aerate the tank without losing the water or drowning the fish. I'm not sure we have the expertise for that here, but I'm sure there are aquarium fora that do.

 

[gazaah]

Yes, from a physics/engineering point of view it will work. My concern would be how to successfully aerate the tank without losing the water or drowning the fish. I'm not sure we have the expertise for that here, but I'm sure there are aquarium fora that do.

The fish welfare part I'm super awesome at, I used to work in the Zoo and Aquarium industry and have maintained all kinds of freshwater and saltwater tanks. The physics of fluid dynamics ... not so much my strong point.

For aeration, I'm utilizing an air bubble curtain. The curatin will be mounted in the access area at the base of the tank, in the three inches of water above the start of the suspended column. This way, there is a large area of gas exchanged water that will be circulated by the pump. All the bubbles will be above the base of the suspended column, so I don't add air and empty the column out!

 

[russ_watters]

The fish welfare part I'm super awesome at, I used to work in the Zoo and Aquarium industry and have maintained all kinds of freshwater and saltwater tanks. The physics of fluid dynamics ... not so much my strong point.

For aeration, I'm utilizing an air bubble curtain. The curatin will be mounted in the access area at the base of the tank, in the three inches of water above the start of the suspended column. This way, there is a large area of gas exchanged water that will be circulated by the pump. All the bubbles will be above the base of the suspended column, so I don't add air and empty the column out!

Great! I suppose the dissolved oxygen readily diffuses throughout the tank? That would have been my other concern. Though I suppose if the fish were having trouble breathing they'd swim toward the area of the tank that is best aerated?

 

[gazaah]

Great! I suppose the dissolved oxygen readily diffuses throughout the tank? That would have been my other concern. Though I suppose if the fish were having trouble breathing they'd swim toward the area of the tank that is best aerated?

Not all fish will figure out where to find oxygenated air, especially if their behavior is to go to the surface and suck a little air to mix it in with the water in their gills. In a suspended tank, there is no air at the top, so that behavior wouldn't help. instead, using a high flow pump will mix the water. I am setting up a shrimp and suckerfish tank, so it won't be large, high oxygen-need fish. However, they'll still be made sick by low oxygen or too much carbon dioxide.

The pump I mentioned before is a MarineLand 290 gallons per hour unit. By aiming the outflow upwards, against the wall of the tall vacuum column, it will force a circular current, picking up the gas-exchanged air as it goes. It's arguable that with so much water flowing past the access area, it would provide enough gas exchange without air bubbles but I prefer to have an excess of gas exchange.

 

[Klystron]

With your experience I imagine you know how to maintain an aquarium. I have two observations.

Despite their adaptations to still water you may want to avoid labyrinth fish and other bubble blowers such as beta splendens and some catfish species that expel air, possibly ruining the vacuum effect. Corydoras and some Chiclid species constantly pop to the surface to capture air bubbles; so, may not be appropriate in the "tower".

Actual petting could remove or disrupt essential skin conditions (slime) and introduce contaminants such as soap and lotion residues. I presume you mean "provide an improved viewing area".

 

[sophiecentaur]

My concern would be how to successfully aerate the tank without losing the water or drowning the fish.

Pumping air (and a small amount of water) out from the highest point in the tank would allow air bubbles to flow in at the bottom. Apart from the fish living in an environment with reduced pressure (<= atmospheric) I don't think they would be bothered. If it was really bothersome, an equalising pressure could be arranged so that the top of the invert was actually at AP. That would mean you couldn't have access ports lower down, of course.

 

[berkeman]

Summary: I am designing a vacuum suspended fish tank.

Sorry if this was addressed already and I missed it, but what happens when the setup loses power? It would seem that about half of the tank's water volume would leak out fairly quickly...?

 

[Klystron]

@gazaah 's plan to pump the water through the aquarium seems correct as long as the water is exposed to air (in the lower structure) long enough for gas exchange. Bubbles are not required for aeration as very little gas exchange occurs at the bubble surface. Air bubbles are introduced for mechanical effect to move the water, avoid stagnation and expose the water to air. Bubbles look nice and reflect light in interesting ways but a good water pump is more efficient and much more directional than bubbles.

Say you have under-gravel aquarium filters. They come with little 'air stones'and 1/4 inch flexible plastic tubing to connect to a gang valve and an air pump. Bubbles rise in the column lifting water from under the gravel. Now replace the air-stone and tubing with a 'power-head' -- a simple impeller driven by emf. Filter efficiency is greatly improved and the output can be directed parallel to the water surface improving gas exchange with no bubbles or visible air flow.

The expert uses external water pumps and filters such as sand or diatomaceous Earth (DE) for aquariums over a certain size, not unlike artificial ponds and even swimming pools.

 

[BillTre]

Interesting project!
I have made something similar to produce reduced barometric pressure to trigger fish spawning in certain kinds of fish.

I don't know enough to understand whether the design on the right would work as well as the design on the left.

They look equivalent to me from a pressure point of view. The one on the left looks to have better access into the inverted area.
The pump you want to use could probably be smaller. I am guessing a small powerhead would suffice.

It looks like you want to set it up and let it go vs. constantly maintaining a vacuum in an automated manner on your system, similar to what @sophiecentaur said. Irregardless, you will need someway to remove air that might get into the tank (from plants, fish disturbances or what ever), perhaps just a flexible tube you could suck them out with.

If you did actively draw vacuum from the top, then many interesting possibilities are available:

• You could have a surface area for the fish at the top as @Klystron described.
• You could put airlocks on top for feeding at the surface.
• You could regulate the air pressure (apparent barometric pressure the fish experience).
• You could easily do water exchanges on a enclosed system (which you could anyway with your open at the bottom design).
• You could aerate the tank with bubbles if the rate of air going in did not exceed the ability of the system to pump air out.

I have used a small diaphragm type air pump that had connections for both sucking in and blowing out air. It cold also suck in water without damage, making it well suited for this task.

I have a friend (an aquacultural engineer) who saw tanks with ports like you have pictured with the ports on the side at some exhibition in Japan. The tanks they used all had a vacuum being drawn from the top
However, it probably would not look as nice a clean and open look as your picture shows.

 

[hutchphd]

I would like to reiterate @sophiecentaur that an air pump will be necessary at the very apex of the tank. Even in the absence of actual bubbles I think the pressure difference will cause air diffusion that will eventually cause air to accumulate at the top. In fact if done cleverly this could be used to aerate the tank!

 

[russ_watters]

Sorry if this was addressed already and I missed it, but what happens when the setup loses power? It would seem that about half of the tank's water volume would leak out fairly quickly...?

@sophiecentaur 's idea seems to have that risk, but the OP's wouldn't include continuous circulation of air through the elevated section.

 

[sophiecentaur]

I would like to reiterate @sophiecentaur that an air pump will be necessary at the very apex of the tank. Even in the absence of actual bubbles I think the pressure difference will cause air diffusion that will eventually cause air to accumulate at the top. In fact if done cleverly this could be used to aerate the tank!

Actually, the outlet at the top could be the top end of a vertical tube with the pump near the bottom level so it would hardly be visible. The fail safe would consist of a large tank volume below the 'table' . Lack of power would just mean the top water level would drop very slowly and the fish would have the same volume to swim in - just less of interest for them to see. Lack of aeration would be the same in any tank with the same exposed surface area as in the bottom tank. A small IPS could supply some bubbles to aerate and a 4G link would warn the owner and they could return home with a flashing blue light.

I could be wrong but the OP is of the opinion that air would not naturally collect at the top in large quantities. As the water at the top is at lower hydrostatic pressure (say 5% lower) than the water at the bottom then Oxygen and Nitrogen would tend to come out of solution (CO2 also) so it will almost certainly turn up there and need to be removed regularly. Edit: The water at the top could even be a tad warmer with the risk or even more gas coming out of solution.

 

[Klystron]

Good thinking. In my experience as an aquarium hobbyist, the larger the enclosed water volume, the more stable the ecosystem and the less maintenance required over time. My most successful aquariums over the years were 70-150 gallon plus small isolation and breeder tanks. Vacuum tanks seem to fall below that limit. I also strive to reduce stress on the inhabitants in my care. Thanks.