I would not use Hydrated Lime alone..That's a buffering agent to be used WITH Aluminum sulfate as a pH stabilizer. I'm no expert either so best have someone like Rainman hopefully post here.
As QA says, I don't believe you want rock substrate to cover entire bottom either.. you need to have interaction between water and soil for certain parts of the foodchain to develop and I'm sure there are other chemically related issues as well.

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