I think taking water from the cell is a bad idea (not sure why though
). I would not think the FC level would change much between the cell and the return.
I loosened up the plumbing ring just downstream from the cell, just enough to let a small stream of (just-chlorinated) water leak out. I can't see how that would hurt anything. But I agree with you that the FC level shouldn't change much before the water comes out the return.
Realize that the cell is not always generating unless you have it set to 100%.
I do realize that. When doing this test, I first turn the cell off and then back on at 100%, and check the voltage and amps on the controller display to make sure it is generating.
Has anyone measured the chlorine "boost" when their SWG is generating?