Hello Sean,
Having two strobes can actually increase the potential for backscatter, especially when you're shooting near the sand like you were at SBI. Honestly, it looks to me more like there's just a lot of particulate in the water, than pure backscatter. However, angling your strobes "out" a bit more, and behind your dome port would help. Also, when you're in an area of high potential for backscatter, try to compose your wide-angle shot with more reef than open water. The reef really helps to hide the unwanted backscatter.
Here's an article I think you will find helpful --->
http://www.uwphotographyguide.com/backscatter-underwaterZig