My jandy 1400 SWG seems to be struggling to maintain chlorine even set at 80%. I run the pump 12 hours a day in the daytime.
I notice that in spa mode the flow light was on but not the cell on or cell resting light. When I set the aqualink to pool , the cell on light came on. Could have been coincidence.

Question is - does the rate of flow vary the output of the SWG? How sensitive oa it to salt levels? I am 2800 so I added 40 lbs of salt- does higher salt levels = more chlorine production ?

Flow rate will not have much effect, except that the SWG will turn off when the flow rate is way too low.

Some brands are sensitive to the salt level and others aren't. I'm not sure about the Jandy.

Much more likely you have some kind of chemical imbalance causing the low FC level. Low CYA levels are the most common cause of failing to be able to maintain an appropriate FC level.

On my Jandy 1400, whenever the flow light is green, either the cell, cell reversing, or cell resting light is also lit. (assuming no service light). I run my SWG 5 hours at night on my 22K pool with a 75% setting and have 5 ppm chlorine in the moring when I check it. My CYA=70. My chlorine level is down to about 3 ppm by evening with full day of sun.

When I am in spa mode, everything shows the same as in pool mode. But I do not have a variable speed pump. I turn down the Jandy unit down to 10% if I have the spa on for more than an hour or two. Afraid of over chlorinating the spa. I leave the spa on all day sometimes when having a pool party.

thanks for the replies. I suspect (for the over-chlorinating concern Sanger raised) that the PB may have turned off SWG during spa mode.
I will post over in Water Balance section about my FC issue. CYA is 80 (tested twice with TFP kit) but I dumped in a large jug of 6% bleach at dusk, took a reading of 3.5 FC an hour later, and early this AM I was down to 2 FC. I will take another reading tonight just for kicks to see how the SWG running at 80% added to the story...

Is there a reason not to go up 90-100% for increased chlorine production?

I think you are right. My Jandy SWG is not hooked up to the controls in the house. When I tested the front board, and read thru the manual, I noticed that there were connections that could be used for remote/automated control of the SWG. My system (about 10 years old now) just starts and stops with the pump. Works fine, just puts a lot of chlorine into the spa when in spa mode.

I could but I understNd these things have a limited life asit is. So running at 100 to cover a problem will shorten it's life by 1/2 if 50% would have done it with proper balance.
But I'm here to learn.

You are on the money!!