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.