The strobe has nothing to do with the focusing...get a focusing light to help the camera focus. You gotta help the camera out here, give it a break or get a Canon A series with a Canon housing. Their focusing system rocks! Which ever way, get a focusing light, this also applies to land photography as well.
Also why is the background so dark? Were you shooting at night? If so, open up the aperture to let more light in.
You DO NOT need a focusing light!!!
Your pictures are not as bad as you might think!!
You are doing well and learning everytime you take that camera down!!!
You need to learn your camera just a bit better and take your time and shoot many shots of each picture and then also try new angles and settings.
What settings are you using??
Also remember the rule of Underwater photography, If you shoot 100 shots and get ten good ones you are doing very well!
You have also added a new piece of equipment and now you have to learn to use it.
PM me if I can help you!