There are a number of difficulties to work with, besides ammonia production at high pH, you are doing fresh water and roots usually need to be in the dark so a kelp/red algae jungle is out. And without much light the yield of any plant will be bad. Perhaps a raft of lettuce on top near a window and cross your fingers that the fish would keep the roots clean but not eat the tender root hairs (hmmm, something says maybe not, better an aquariast) , and that such a high pH wouldn't be a one-two punch with low light to knock out the plants quickly. The Asians eat a lot of Wolffia duckweed...

Spirulina is highly nutritious, but due to the proximity of the fish, things like E. coli, etc., I'd grow it as fish food...

The difficulty is you want to adapt your plants to your choice of fish, but people doing aquaponics have enough trouble making it work by adapting the very best fish to plants, both sequestered in their appropriate media.

Maybe a Spirulina cage the water can diffuse across but not the algae (30-50 micron = 0.03-0.05 mm =~400 mesh) would be simple and rewarding fun project!

If you are really intent, check on the conditions required for watercress and see if you can meet them halfway. Someone else probably knows if this is doable with Watercress or also Chinese Water Spinach both are about as good a compromise as it gets for high pH. Just be careful since some really nasty parasites (alien brain eaters LOL unless it is personal, then SOOL) according to the CDC come from water plants grown in these sorts of environments

This post was edited by PupillaCharites on Wed, Sep 4, 13 at 19:28

I don't know about brain parasites, but before anyone gets too scared of fish poop, e coli doesn't come from fish. It requires a warm-blooded organism in which to survive, at least for very long. The only way a fish tank is going to have e coli is if its food was contaminated. Worms fed as food can carry it through the soil/compost stuck to their bodies, but to get sick from that through an aquaponics farm would be a very remote chance, probably less than with lettuce from the grocery store.

'alien brain eaters' was a LOL, but I think caution is a good idea when the systems are linked. Clueless what the fish eat but if it is live, E Coli or similar pathogens can colonize the intestines of the fish and its poop and it is not clear whether this filtration will block that.

Agreed that the liklihood /danger is not great with care. If you could stike a plant/animal balance, the high pH requirement is probably the hardest problem with this system (and I naively assume in real aquaponic systems the pH is adjusted somehow or just the fish are lower pH tolerant) and still like the idea of having a little reserved area for Spirulina which almost uniquely loves high pH and could be a fish food garden. Since the fish will be around 80 F degrees, an idea would be to place an attractive light over the garden that locally/surface warms as well, and that the muted light maybe cast rays serving double purpose of a diffuse light and warming/lighting the Spirulina only (NASA did something like this, didn't they).

I don't know the pH tolerance of wheatgrass, but it will grow in pretty low light and is worth checking out for this. Are there any commercial products aquarium farms on the market to get ideas from?