Green Heliofungia / Plate Coral Puffing up

[ashleigh234]

I have had a Green Heliofungia for 3 weeks, he is up on a flat rock with medium flow. For the last 3 weeks, from at least 7am it would be opening up and by 9-10am would be fully open as per pic below, sometimes larger than the pic as it looks like he doubles in size when fully open. Then about 4-5pm retracts to a smaller size, but tentacles are still waving about.
Normal pic:

This morning I came downstairs and it looked like the below pic, then I went upstairs for half an hour, came back down and it was normal again (like first pic), then went 4 metres to the fridge, got fish food, returned to tank, and bam, is back looking like the below photo:

Seemed to return to normal not long after.
Was it trying to move? If it sounds like it I may put him on the sand, although there isnt enough flow where i would put it, as it gets to big during the day the only spot it will fit is a low flow area.
Tank parameters havent changed and all fish/other corals are fine. The only thing that I had done was 2 days ago put a small rock with a mushroom on up on the rock near the helio, would this have upset him?

 

[mason]

far too many variables to pinpoint, and nothing specific to that genus in my opinion. I've seen fleshy corals twist and contort in different ways and sometimes just like you've pictured, I truly can't guess what they are doing I just know it's not out of the ordinary especially per your test results, and the fact this was transient in terms of polyp morphology.
B
I will say though my lps do that sometimes if I topoff midday, during full expansion, vs night topping where they are all closed up in my tanks.