CA, In my marine pics I've found the best effects are a mixture of 2 main things: the colour/texture/shape of the surface i.e. sea bed and the decay distance. Sliding the volume colour button to white allows the subsurface colours to show through more, and is very manageable via the small surface preview window.
The transparency value obviously has a major influence but it's very dependent on how close to the surface you are and the scale of the scene.
Hope this helps.
Kevin F
