Uave had it about 2 weeks now. Have an aqualife t5 flourescent with 2. Sun ,2 blue and 4 led nigts on it.. Yes looks like a feeding response as disk stays same size but it sends tenticles out top
Try offering it some food during the day. Introduce a very small amount or drop some pellets on it if you have no hermits to harass it. It's opening at night because that is when a Fungia would normally eat.