yes the shrimp walking over it can cause closure however IME they should only close for a temp time and open once the irritant is gone , you may find that you will need to do successive dips to remedy this if there is something on them . You will not want to do this more than once or 2x aweek ... after the dip gently swish them around to just drop anything off that came loose from them .Try to get those nitrAtes down below the 20 mark by increasing your water changes to once a week . I keep my spg at 1.025 on our reef tank ...Just becareful that the syringe from the test kits have no reagent on or in them as this will further irritate an already irritated colony. Try to keep these away from any other corals that could be giving off a bit of a chemical warfare, this can also cause them to close up . Try adding new carbon, chemipure or purigen (carbon should be change monthly or so depending on your bioload and rinsed weekly if you have a larger bioload replacing biweekly should be fine still rinsing weekly , The other medias should be rinsed weekly and changed out every 3-4 months IME ) I have already lost zoas for no appearant reason .
What kind of lights are you using PC
, NO , MH
, T5 or other ?
How old , are the bulbs and when was the last time they were replaced ?