What test kit?
Having your calcium at 520ppm will not harm anything. Over the next couple weeks your Ca will naturally come down to under 500ppm. Monitor your Alk and maintain it at 8-10 dKh to prevent precipitation of Ca.
If you are worried about it do as Kien suggests and buy some Instant Ocean salt which has Ca levels typically around 380ppm and do dome water changes.
Stir your sand as it has a tendancy to solidify and clump at 500+ ppm.
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