Harvey,
I would put the new fish into a floating basket and let the new fish get used to it. This way they can see it but can't get at it and the novelty wears off. Keep it in there for a week to ten days and in theory you should have no problems after that. This has worked for me in the past.
If that doesn't work, you definately have the room for more rock, thus creating more hiding spots and that way the fish don't always see each other 24/7.
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Greg
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