My BTA is driving me crazy is this normal "pic"

[JMLufkins]

will look like this

and then the next thing i know it looks like this

is this normal

 

[finding nemo]

Yup, totally normal, they will inflate and deflate all thru the day to replace water and poop.
Keep in mind that your clown may also be irritating him but looks like the size ratio is fine.

 

[Sports Girl]

Off-topic, but nice coralline growth!