Thought I might add to that comment about not wandering too far from the boat...
Some of the best things I have seen diving over the last 30+ years was right under the boat. In the flower gardens, I saw both a hammerhead and a manta ray and I had the boat within sight.
On my last night dive @ TnC with Aggressor, I stayed literally under the boat while everyone else was off and away and I had 2 sharks and a cubera snapper (google that bad boy) circling me the entire dive.
A couple of other notes:
1. It is impossible to get lost when doing an oil rig dive and you often get the juvenile silkies come in close.
2. At Stetson bank, they run a guide line to the wall. My suggestion is to follow that guide line to the wall, swim upcurrent until you have 2000 psi left, the swim back same path until you find the guide line. Use the remaining 250 making your way back to the safety stop and end the dive at 500.