You should have your stenner get its power from a source that is only hot when the main pump is on.
With a fixed pump, if you have an EasyTouch, JandyRS, etc. you could wire it into the control panel and use the systems scheduling features. If you are setup for the app, you basically could control the feed time(Scheduling), or even set it up as a Feature that you could turn on anytime via the app.
- - - Updated - - -
Does this tank have coloring in it, or enough coloring, to shade the chlorine from UV?