Duncan Only opening at night

[CJ Monty]

I have had this duncan for 3 months now. Last week or so it has been close tight when the light is on and opens when just the moon light is on. Makes me think it is not a flow issue, but perhaps lighting? It is on the sandbed of a 24" deep tank. My zoas, palys and euphyllia seem fine.

Do duncans like less light?

 

[AdamNC]

Possibly something is picking at it during the day? Mine love med to high light.