I've tried Oceans wonders Coralline Purple Coralline and CorAffix (super glue gel). The glue works ok to glue frags on plugs but the putty does not work to attach frag plugs to rock.
With putty you have to work it in to the rock use a toothbrush handle to press it in the pores of the rock
Also look for the putty that is 2 seprate sticks that single stick stuf is just horable
I smear some SuperGlue Gel onto the mounting point in the tank. Then put some Gel on the frag itself. Set the frag in place, and it works like contact cement. If you are mounting a larger frag, hold it in place for a minute until the glue thickens up. Smaller frags grab and hold within a few seconds. Works great for me.