Phosphate Reactors.

[danny zubot]

I have read that they can have adverse effects on some corals.

I don't have the information to back this up anymore but I heard a reason for this a couple of years ago.

Some PO4 media use various elelments as a base which aren't good for marine aquariums. I read that some use a Mg base which can throw your other levels off, while others use various heavy metals that would only be suitable for freash water use. Sorry I can't back up this claim at this time, just offering a plausable explaination.