What can hinder absorption of calcium in corals?

[XeniaMania]

I could have sworn I've read something about this, but Googling kept giving me coral calcium to put in your water results, so I'm hoping someone here knows what can hinder the calcium absorption in corals. Thanks.

 

[reverendmaynard]

Phosphates. Studies have shown levels as low as .03ppm can inhibit calcification in certain sps species.