I agree that live rock is nicer and a better source of bio-filtration than limestone but if it has any color or growth on it I would use some of the nicer pieces and add live rock to it. My 55 reef at work is 75% central texas holey limestone (1 big arch piece) and is nearly completely covered with coraline, sponges, and misc worms and critters. I used this in my first tank and have always setup an additional tank after I got nicer live rock because I didnt have the heart to let it dry out .

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