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Re:Kevin Conlin's tank design




 Kevin Conlin <kcconlin at cae_ca> described this tank design in Digest VI #55:
>
>                           Aeration chamber
>
>                        |                    |
>          ---------------      Nutrient      ---------------
>          | _____________   -> Water Flow -> _____________ |
>          | |           |____________________|           | |
>          | |                                            | |
>   |      | |                                            | |     |
>   |    -------                                          | |     |
>   |--- |     | ------- Water Line --------------------- | | ----|
>   |    |     |                                          | |     |
>   |    |______                                          | |     |
>   |      | |   Powerhead                                | |     |
>   |      | |                                            | |     |
>   |      | |                                            | |     |
>   |      | |                                            | |     |
>   |      | |                                            | |     |
>   |      | |                                            | |     |
>   |      | |                                            | |     |
>   |----- | | ------------2" Gravel -------------------- | | ----|
>   |      | |                                            | |     |
>   |_ _ _ | |_ _ _ _ _ _ _ Fine Mesh _ _ _ _ _ _ _ _ _ _ | |_ _ _|
>   |                                                             |
>   |                    2" Root Growth Area (no gravel)          |
>   |_____________________________________________________________|
>
>
>Plant roots grow through the fine mesh into the aerated nutrient
>solution circulating below the gravel.  Relatively few nutrients
>(hopefully) will make it past the mesh, through the gravel, and into
>the water.  Nutrients that escape will be sucked up by hornwort or
>duckweed or something similar.  Oxygen diffusion from top & bottom
>would keep the gravel (or even sand) from becoming anoxic.  An
>ordinary canister filter would take care of the water above the
>gravel.
>
>The fine mesh could be standard UGF filter plates (the square interlocking
>kind) or even plastic speaker grill, supported by short lengths of PVC pipe.
>Any open plastic container would work as the aeration chamber, which could
>contain bioballs or something similar depending on the degree of aeration
>desired.  A valve of some sort at the outlet of the powerhead could be used
>to decrease the flow rate of the nutrient solution.  As for the solution
>itself, just add your favorite fertilizer to the aeration chamber at the
>recommended intervals and monitor iron and nitrate as usual.
>
>Comments?

The pathway of the nutrient water flow above the tank water level will have
to be completely air tight.  If air can get in, the weight of the water
column above the tank water line will force the nutrient solution up
through the fine mesh and through the gravel into the tank water.

I suspect that diffusion along with transpiration by the aquatic plants
will cause the mixing of the nutrient solution with the rest of the tank
water faster than you expect.  However, only setting up the system and
testing the tank water for some nutrient, such as nitrate,  will tell for
sure.  It sounds like an interesting experiment to try.  Go for it!


Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174