Shells releasing phosphates?

[Apet66]

I have a few medium size (3")empty snail shells in my reef tank. My question is, over time will they break down and release phosphates? I'm noticing some Cyano forming around them in the sand where they are laying.

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[Mike J.]

Snail shells won't release phosphate. I suspect that the cyano collects around them because that's a low flow area.