I have an ATI Sunpower four bulb with Reef Brite XHO Actinic Blue. With all four bulbs on I run the Reef Brite at 70% to get my desired PAR. The four bulbs I have are Blue Plus, Actinic, Coral Plus and Blue Plus. Ordered back to front with the Reef Brite attached to the front of the ATI.
At 7PM I turn one set of bulbs off (Actinic and front Blue Plus) and ramp the Reef Brite up to 100%.
At 8PM I turn the other set of bulbs off, leaving just the Reef Brite on at 100%.
The corals I have stay open.
I guess the key is to not have the lights dim to much or to quickly that the corals close.