Greetings Posers!

I am trying to create a scene in the bottom of a pool of water.
I have set up my characters and did the nice tile background and floor of the pool. I rendered it but can not get that "Caustic" effect caused by light flowing through surface water ripples.
I placed a ripple image above the scene and out if camera view and shined a bluish spot through it down onto the subjects but still no ripple shadows. I varied the transparency of the ripple tex and cranked the shadow up to max on the spot light. Still nothing.
What am I doing wrong?

BTW I am using Poser 4. I have done similar shadow effects but never with water so this is kinda new and i am flummoxed as to why it is not working.

I thought I could make a b&W version of the texture with a trans map so it will cast a stronger shadow but not sure if this is a good solution and if not don't want to do all that work (I am a bit slow with that stuff) to do it if it's not going to work. Any help would be appreciated but the "Pros" here!
:)