bubble coral acting strange.

[DEAD_BY_DAWN]

so i have had this bubble coral for three months now ,and half of it has acted strange,it will inflate in deflate itself quite a few times during the day,expel its zoonanthelia about three times per week ( there is no loss of colour), feed once a week,waters great cal-450ppm,alk 12dkh,sal1.026,nitrate under 5ppms,ph8.1,lighting is on my user info any ideas is this normal ,in the end it does look healthy.so why only half of the coral is acting odd ?