I had the same problem when I 1st got mine from Gilbert. I had them toward the bottom of the tank near a power head.Then I moved my rock with 4heads higher toward the top, and away from the Koralia3 power head and they opened up nicely. I started dosing with B-ionic last week sunday and 3 of those 4heads already splitted into 2 each.
So you might want to move them to a not to strong water flow, and see if that makes any difference. if it doesn't work just let me have them