Ok, perhaps I'm a moron, that's entirely possible, but I thought the 980Ti was CUDA.
Blender shows GPU as default (which is grayed). I go into system settings, it doesn't show Cuda.
However I check the "FlipFluids addon" and this clearly shows the GPU is seen.
I'm on Mac 10.12.6, 12-core, running Blender 2.79b.
I've searched Google, NVidia website, reinstalled drivers, deleted Blender/reinstalled.
And when I switch to OpenCL it crashes.
I'm stumped. thanks, alldaron