I have a scene that I can separate the lights and the base geometry and render and have the volumetrics from my lights look great at around 32 samples on the ENV fog shader. but once I place this in the main scene and render I get grain in the fog that I can not get rid of. I have tried taking the sample up to 512 and it has zero effect I have tried increasing the number of steps up to about 200k and the distance down from 1 to .001 and it has 0 effect.
I have no idea how to use a Gizmo for the fog I just used the ENV fog on the Volume shader port of the a SG with the Vray material opacity turned down.