I've heard mixed things about the whole discus/shrimp issue- to the point that I think it just depends on the discus. If they're captive-bred they may be a little less likely to be used to hunting down shrimp, but that's just guesswork on my part.
I'm personally planning on stocking with the 20 of the biggest adult RCS and amanos I can find and see what happens.
I'd nix the rainbows, I believe they prefer harder water, would do better in a larger school, and the biotope snobby part of me says they don't belong in a discus tank (neither do RCS or amanos either but what can I say- I'm a hypocrite! LOL)
Other than that, it looks good to me- you could try oto cats if you're worried about the shrimp.
Oh- and if you want to KEEP hatchets in your tank a canopy isn't optional (if you don't want a canopy, my cat would love to come visit your house sometime
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