Can you post your most recent complete set of test results? You mention Bioguard in your signature. Are you still using this? I agree with PoolGate you can add the cell with no problems. If you SLAM after you install we recommend you turn off the SWG while SLAMing but that's to help you figure out how much chlorine is being consumed not to protect the SWG.
Yes, I haven't changed anything except adding the Intelliflo. This morning when I tested FC it was at 15 which was down from 16 last night. I just tested again and it's down to 7.5 in only about 5 hours. Water looks perfect.