gluing frags is kinda tricky, and you will get better over time/practice so make sure you get extra glu
You will want to dab the frag onto a paper towel to kinda dry it, then apply glue all over into a gob... then you will place it under water to the rock you want and kinda twist/smoosh the frag into place and hold it...
The glu doesnt really glue like it does when all things are dry.. but what will happen is the glu will get hard and kinda mold around the nooks and crevices of the rock and when the glu is dry enough it will hold...
you can get frag rocks, or plugs or discs or you can smash a rock into bits and use them.. that way you can glue the frag to the rock outside of the water, then you can just put the frag and disck/rock whatever back on top of the rock... the larger frag rock/plug will help hold the frag in place...
as for the bulb and ballast issue...
you need to make sure the bulb you have matches the ballast you have...
some ballast are hqi, some arent...
they might have numbers/designation like m59 or something like that... (sorry, i never got that much into the ballast issues)
but the bulb will need to be compatible with whatever ballast you have... or it will not fire all the time...
some ballasts are referred to as magnetic, some are electronic, etc...