I like seaweed but I'm happy to buy the dried stuff - I think the kind we get is grown somewhere off the coast of Europe rather than in Japan but will check the packet.
If you google there are a few sites about growing it in a fish tank (mainly for people who keep saltwater fish) but I would think it would be difficult to make it nutritionally equivalent to the stuff from the sea which is meant to have various trace elements etc I think.
You mean if you didn't put the right trace elements in the water it wouldn't grow at all? That's possible, I don't know.
It seems you can buy "preparations" containing the minerals found in seawater to add to salt water aquariums (for the benefit of the fish I imagine) as mentioned here http://www.liveaquaria.com/PIC/article.cfm?aid=75 Whether growing seaweed in that would result in something fit for human consumption I don't know.
very interesting, i never thought that it was possible to grow your own seaweed. im very interested in just harvesting my own seaweed, but im too far from the sea for that at the moment. i hope growing it will work for you!