Sherry,
First off, I want to stress that I feel your pain, and a lot of us have gone through this.
I started with a C5000z and a Sealife and had the same problem.
Since I am landlocked, I did A LOT of pool work. I bought some tub toys:
drilled some holes in them, and weighed them down with screws.
My local county pool let me use the deep end in the mornings.
I basically lined them up on the floor of the pool and started taking pictures. I learned strobe placement this way, as well as proper intensity. It gave me a really good baseline.
Like others have said, I learned to shoot manual. I did not have TTL, so I had to adjust the strobe. It simply took time to learn range, and the next time I went diving, there was a tremendous improvement.
One website I recommend is:
underwater strobe positions|Underwater Photography Guide
This particular page deals with strobe positioning, and it will help you learn how to minimize the spots. The website is full of valuable info.
Secondly, like others have said, I HIGHLY recommend you purchase Adobe Elements. It has EVERYTHING you would ever need to edit your photos. Fortunately my best friend is a wedding photographer, and taught me a lot. I would talk to any friends that are photographers and see if they will give you some lessons. Do not let them tell you that you need photoshop. Elements has everything and is $100.
I now have an E-620, but I still take it to the pool and work with my rubber duckies!
Breathe in, breathe out, move on...