Frogspawn Coral with Open Mouth?

My frogspawn during the day is absolutely georgious! It has 4 heads and 2 of those are starting to split! So I know it's healthy and is about the size of my hand during the day when fully open. When the lights go out and it starts to retract the one head that just finished splitting not ong ago has gaping mouths. Both heads. Like extremely wide! but it's only at night this happens and only a couple hours after the lights go out but then another couple hours later everything is back to normal. I'm not worried because it is so healthy during the day and all my parameters are perfect, except my nitrates which are around 5-10ppm. But dispite of that everything in my tank is extremely happy! Why does the frogspawn have an extremely wide mouths and only at night?

 

might be waiting for food to fall in my candy canes do this at night too, I feed them a flake and they close haha, could be it, but might just be open for no reason