Scatter GI - enables the tracing of GI through the fluid - the engine(s) currently specified in the GI option will be used to accelerate the tracing
Scatter bounces - when Scatter GI is enabled, this controls the number of GI bounces that will be calculated inside the fog.
Simplify textures for GI - when this option is checked V-Ray will use a simplified method for calculating the GI when rendering parts of the liquid that are textured or are being faded out.
Step size - determines the size of one step through the volume of the liquid. Smaller steps produce more accurate results but are slower to render. In general, dense volumes require smaller step sizes than more transparent volumes.
Max steps - specifies the maximum number of steps through the liquid
Texture samples - determines the number of texture samples for each step through the liquid. This allows to sample textures more accurately than the volumetric lighting. It is useful in cases where the textures vary much faster than the lighting itself (e.g. for detailed fractal textures).
Cut-off threshold - this parameter controls when the raymarcher will stop traversing the volume. If the accumulated volume transparency falls below this threshold, the volume will be considered opaque and tracing will be aborted. Higher values make the rendering faster but may introduce artifacts.