I used to think PH adjustment was very important - but the treatment is short term, and the zoos hold so much water that they came from - I have never seen it truly make a difference to teh zooanthids, or other soft corals.
Additionally the ph difference may help to further shock/parasitic bugs that you are trying to get rid of. They will react faster to the different chemistry of the water than will zoos.
Bear in mind that most to the zooznthids come from near shore, lagoons and similar, and they are subject to dirty water that varies in salinity and PH quite often due to rain and run-off.
brifirst...WHICH Coris? Coris is a genus of wrasses of which there are many different members.....
T