I Know you said your params was ok but can please state it bro..Hmm zoas are hardy could also be due to pest/Lights..try Moving them to bottom and giving them a Coral DIP..That would kill pest and not eggs..get a Sixline Wrasse..Would Also help.. with eggs..If you have time stalk at night see any thing crawling zoa spidets,nudis or anything.. But a coral dip would kill them off,,Hope this helps bro do update us!