The 10-17 can be a challenging lens to get shots with because you have to be very, very close to your subject. Most of my good shots with that lens are taken within 2 feet of the subject, with many of my favorite shots touching or nearly touching the port. This applies to 15ft whale sharks, as well as sea lions and octopuses. For larger domes (8in+ diameter) the closer the better, and with small domes, within a foot or so tends to give me the best results. Ideally, you put the lens on 17mm, look through the viewfinder until the subject completely fills the frame, and then move closer and zoom out until you like the framing.
The other issue that is inherent with shooting that close is good lighting. You will need to effectively balance ambient light and strobes (2 minimum for large subjects). The only way to learn that is to go out and practice. Ideally you dive with the same subjects several days in a row and you can check your results each evening to see what works and what doesn't.