HELP?! Anemone dying..????

Newbie to the saltwater hobby... bought this live rock 2 weeks ago and it had this little guy attached.

He was doing really good, every couple of days he would snag a particle of the frozen fish food and suck it in side him.

He grabbed a rather large piece of dry fish food today, and about 3-4 hours later I found him like this.

What is this large white mass by his mouth? He sucked it inside for about 15 minutes and then it came back out.

Should I be freaking out?

 

Hi and welcome to 3reef,

Anemones are such weird little creatures. It's very common for newer hobbyist to become very concerned when the anemone changes shapes. The white is gastric cavity, no much in the way of anatomy for anemones.
How long has the tank been running, do you know the type of anemone. I can not get an ID off the images.
Looks like it's either a bubble tip or a rock anemone.
When you notice a stressed tank inhabitant always check basic water chemistry.

 

+1
Could even be a mojano, looking at tentacle shape and coloration.

 

The tank has been running 2.5weeks. Did a water change 2 days ago, Clown fish doing very well. all water perimeters are okay,
ph at 8.2
salinity 1.023.
Nitrates a little high, at 5-7ppm
Nitrite at 0.
Ammonia at 0.25.

Running a aquaclear 50 with foam, bio max and carbon insert.