Corals arent opening...

As per the title, the corals that I had in my tank are not opening as much as they used to. There corals that are particularly affected are my hammer coral, scoly and brain coral. I had a cyano problem and added biopellets to help out with the cyano. Nothing else has changed in the tank, could the biopellets be the cause of the problem? Or is it another suttle change that may have occured?
Thanks
 
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