Urban Aquaculture building project

So here's the deal: I am living in Toronto, and have two 12x12 (approximately) roofs that I can potentially use for part of a greenwater aquaponics setup. I am currently getting the load-bearing capacity of the roofs assessed, and I'd love to know, if anyone can tell me, what is the minimum depth required for a system that would comprise these two surfaces. The goal is to produce not only aquatic plant matter for the greater system based on the ground beside the house and in the backyard, but also to host elements of the system that would likely comprise smaller feederfish, either an omnivorous species that would feed on the plant life as well as the insects that drop into the water, as well as the larvae of those who seek to breed there (very important, as West Nile and whatever else is a topic of paranoia around here, and it's free food), and perhaps some kind of crayfish and filter feeder. I am not worried much about oxygen depletion, as there is a one-floor difference between the two shallow rooftop ponds, and a 1.5 storey drop to the ground, and I will be using pv and wind-powered recirculation with household backup.

As soon as I have the rooftop capacity figured out, I can see how far I can take this system. My "aim high" goal is to be able to farm sashimi-grade salmon and some variety of large catfish (channel?). I'll be happy if I get rainbow trout and brown bullhead.

The building materials I'm looking at currently are warehouse pallets (for tank walls and perhaps inverted on the roofs to distribute weight better) and pond liner. I am probably going to fill the void spaces in the pallets with wood chips or paper waste, sealed from moisture in vapour barrier and probably mixed with borax. While for the in-ground pond, I will be using pond liner on the bottom and three sides, I am also hoping to use something of a hugelbeet on the final side to connect a gradual entrance to the pond with a natural transition to the garden, which will be fed by wicking or drip lines from the aquaculture system.

I would appreciate any insight.

-CK

Hi Chris,

I'm having trouble picturing the system you have in mind. If you can upload a drawing or something I would love to see it.

On rooftops in Toronto you're likely to have to deal with a lot of cold. That's a concern.

There's no real rule with the depth of fish tanks, though repurposed freezers work well in the cold.

People generally recommend a grow bed depth of 12 inches, to give the bacteria enough surface area to live on so they can convert ammonia to nitrate.

Jeremiah Robinson wrote:Hi Chris,

I'm having trouble picturing the system you have in mind.  If you can upload a drawing or something I would love to see it.  

On rooftops in Toronto you're likely to have to deal with a lot of cold.  That's a concern.  

There's no real rule with the depth of fish tanks, though repurposed freezers work well in the cold.  

People generally recommend a grow bed depth of 12 inches, to give the bacteria enough surface area to live on so they can convert ammonia to nitrate.

Plants can take ammonia from water directly so theres no need to have bacteria and further conversions to N02 and NO3.