Drilling hole in glass aquarium-

Hello,
I've been trying to drill a one and one eighth inch hole in the side
of a glass aquarium but everytime I get near to the end of the hole the
glass begins to crack. I am using a Diamond glass hole saw (with a drill
guide) and applying water for lubrication according to the manufacture.
They also suggest using a drill speed of 150 rpm (which I have no way of
telling on my drill) and applying light pressure. Has anyone in this group
have had any success with drilling their own holes? Thanks! -MIKE