Why is sulfate going down on watts chemistry?

This sounds like a test question.  And when you say "sulfate" I assume you are referring to the dissolved nickel metal portion of the nickel sulfate liquid, right?

I've seen sulfate drop in a nickel bath due to a low amount of anode surface area.  If I add more anodes to the bath (or remember to fill up the baskets in the first place), I require less nickel sulfate to be added over the side.  Chemically, I can't point to the exact reason why this happens, but I've seen it repeatedly, especially on barrel lines where the cathode surface area can be huge.

Along those same lines, I've seen a bath or two that "grew" nickel sulfate over time.  We removed a few anodes and the growth of the nickel sulfate slowed.