Chris is correct, 350ppm is acceptable; however, I would recommend higher levels to act as a "buffer" against mistakes. It is very easy for Ca to drop below acceptable limits when you have a fully stocked tank. If you can insure that it won't fall below 350, you're fine.
Also in question is balance. With an alk that high, your "balanced" Ca should be about 430ppm. A one time use of CaCl can boost your Ca to a more balanced value.
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Brad
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