ive 5 small colonies of zoas in my tank. 2 colonies were doing great for a while. now all dont open up as much. 3 havent really opened. a few of the colonies seem to be dying back as the lighting and water flow hasnt changed. dont know what to do. i added a nitrate removal pad a month ago to help manage the nitrates, and it worked. but some werent doing so well before then either.