Triple bridge from salt to tropical to fresh?

Kyn

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Hi all, newbie here.

I'm building an indoor vertical garden, approximately 2m x 4 levels of guttering with a "Donkey Kong" angled approach, with water pumped from the first tank 25L tank to flow down and return to it, to be pumped back up. Initially this will contain added nutrients.

I have another two tanks of 36L, 25L and am collecting another ~30L tank.

My hope is that it is possible to setup the tanks to provide the nutrients and clean the water, without the need for filters.


I'm expecting that, if possible at all, this will involve a selection of aquatic plants and microbes, small aquatics creatures and other things, though I would prefer to avoid any fish if possible due to a family members allergy.

I have done my research and understand water bridges from one tank to the next, but I'm unclear of the steps required to ensure the salt isn't transferred from tank to tank, as I don't want that entering the plants water supply. If I can ensure the salt water stays below the bridge entry with a fresh water layer, or something similar, that will do the trick, but this is my first time doing something like this, or anything aquatic (ambitious, I know) and I accept it just may not be possible, especially with such small tanks, which are low profile to allow as many growing levels as possible.

If I have to drop salt water from the equation, so be it.

Thanks for any advice you can give, and please forgive any silly aspects to my design.
 

Formulator

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Its a really cool idea, but I can unfortunately tell you without a doubt that its just physically impossible to do what you are proposing. You just cannot separate water with water.

Saltwater is just water full of ions bouncing around, like kids in an inflatable bounce house. Fresh water is like an empty bounce house. If you connect that empty bounce house with the one full of kids, what happens? The kids spread out and bounce all over in both houses! The same is true of saltwater. If it touches a body of freshwater, the ions spread out and now you just have one big body of saltwater with lower concentration of salt (spread out kids/ions).

I guess you could have ion exchange through an osmotic membrane, but that will just delay the inevitable equilibrium of the entire system as lower salinity saltwater. Probably close to brackish.
 
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Kyn

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Its a really cool idea, but I can unfortunately tell you without a doubt that its just physically impossible to do what you are proposing. You just cannot separate water with water.

Saltwater is just water full of ions bouncing around, like kids in an inflatable bounce house. Fresh water is like an empty bounce house. If you connect that empty bounce house with the one full of kids, what happens? The kids spread out and bounce all over in both houses! The same is true of saltwater. If it touches a body of freshwater, the ions spread out and now you just have one big body of saltwater with lower concentration of salt (spread out kids/ions).

I guess you could have ion exchange through an osmotic membrane, but that will just delay the inevitable equilibrium of the entire system as lower salinity saltwater. Probably close to brackish.
Thanks for you reply. It's pretty much what I figured.

Fresh water it is!
 

Doctorgori

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I think so, I imagine at least one tank with lots of light and nitrogen hungry veggies…
maybe a “filter feeding” stage with clams, sponges, whatever …
…maybe even a “deep sand” stage for de nitrification, filtering, sifters, et et
Anyway, sounds like a cool build thread
 
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