A very potent way to get them to open is seafood mix... Prawn, Sliverfish, sotong and blend den mix with rotifers, cyclopeeze and mysis... Squirt at the sun coral on the time that you want it to open... After a week, it will open at the time... After 1-2 months, it will remain open...
PS: Skimmer need to be oversize and it will go crazy...