Thanks for your reply --- you got me thinking...

With my current plumbing, in pool mode, water is drawn from the pool skimmer, filtered and heated (either solar or gas) and it then enters the return diverter valve and is directed to either the pool return or the spa return lines. The SWG sets between the return diverter and the pool return lines. When the SWG is on, it injects chlorine into the pool return line, but not the spa return line. The spa bypass draws water upstream of the SWG, and therefore the spa is never chlorinated directly from the SWG, it gets chlorine by replacing spa water with pool water. If I filter and pump long enough the spa water will be replaced with pool water and approach the same FC level.

I've been considering moving the SWG upstream of the diverter with requires two chlorine settings, one for the pool and one for the spa, but you gave me another idea.

What if I added a spa bypass line downstream of the SWG? Doing this would allow me to send some of the chlorinated water directly to the spa. In other words, with the new bypass line closed the system would work as before. With the new bypass line open, the spa would receive additional chlorine directly from the SWG. Depending upon how much water I diverted from the SWG would determine the higher chlorine concentration in the spa. In spa mode, no chlorine would be injected.

Comments appreciated....