Thank again bro, and nice meeting you and your wife. Ankle is healing, slowly ...
Here's a pic of the lamp i used (as mentioned this is existing lamp i have, just lucky that i could remove the head and plug in the PAR38 ...) i put some details about the fixture. This is also clamped in the adjacent computer table. The ikea tertial should also be ok already, since it seems sturdy and also not expensive.
On my fear of it dropping directly in the tank (though so far hasn't moved down one bit), i offset the lamp head to be just on top of one of the corners, so if it drops down, it goes smack on the tank (won't drop that strong anyway if ever). Just had to make sure i tighten the locks real hard. When not in use i can easily swing the lamp away from the tank towards the back wall.