Victory! Took the ballast back to the LFS where I bought it. They seemed skeptical but exchanged my ballast. Got home, plugged it in, and viola - fired up instantly.
Also ran a freshwater plumbing test. The pump is outputting WAY faster than the tank drains. And the flex hose drain is leaking a little - so we'll be swapping the bulkhead for a better one that allows us to go full (wider) pvc on the drain.