Attached Link: Liopleurodon Image

 Thought I'd chime in here.

I do quite a bit of underwater in Vue. Currently using 7.5
I've never deleted the sun, for what it's worth. A couple of tips: Make sure your volumetric light is above the water surface. I also find that angling the light makes a big difference in the caustic effect. Agree with the above comments about making the scale of the gel smaller and also increasing the contrast, though rather than going into the function editor, I've done it by going into the color map and adjusting the slider. Also, increase the volumetric light's spread can be effective.
The other thing is that you may need to have more than one light. In the attached image, I used two volumetrics to get the light beams, then another 3 lights non-volumetric but with gels attached at a very high level (300) to get the light patterns on the animals. These non-volumetric lights can be placed below the water surface.