The trickiest thing about managing Rate on this puzzle is the fact that the water and quicksilver want to be applied to opposite sides of the product.  Our first attempt used 7 arms and 10 track to do the job. Expensive, maybe, but pretty small, so we were satisfied with that. 

Noticing that our solution was very close to fitting inside a size 5 hexagon, we idly started tinkering to see what it would take to make a RBG solve.  In doing so, we discovered this method of handling the reactive water, using only six arms and eight track.  Pretty good savings! 

For the record,the notorious RGB solve *did* work with size 5.