[tom]

dark reflections are showing up the reflected bright caustic particles i think
like a dundruff on the hair

[Tyrone Marshall]

I have had that very same problem with a render I made with a building concept design that is sitting on top a shiny cobalt ground plane- the reflection and the casted reflection back on the object all have noise.

[Mihai]

Caustics seen in reflections, especially a perfect specular reflection like you have on those spheres will take a long time to clear up. You could try decreasing the reflection in the spheres just a little bit.

[Mihai]

You assume correctly