turn your SWCG off for a few days and allow the FC to drift down.
This ^^
By watching the chlorine drop, you’ll gain more confidence in your results. Then turn it back on and watch it go up. Again, by repeating the test and having it match your actions, you’ll gain the confidence/expertise that you need in order to trust the process.
I would definitely spend some time researching what SWG you have. It looks like mine - a Hayward. It would be good to ensure you know exactly what you have. As was pointed out, you may have a very high capacity unit compared to your pool size.
Also remember, that there’s two dials to control the chlorine from a SWG. The knob you have set at 30% and the amount of time you run your pump.
Also, also, not sure if you have a solar cover, but when I use my solar cover, I don’t lose as much chlorine. For example, I have my SWG set at 50% and my pump runs for about 14 hours. We’re not swimming yet (live in MI) and my chlorine is up around 15 and rising this past week. I attribute that to cloudy conditions and the cover. In the summer when the cover is off most of the day, the suns shining and we’re swimming, there’s no way those settings will be enough to keep my chlorine so high.
ETA - I just looked at your picture and the SWG says sanitizer 40. I’m
guessing that means you have the model for a 40K gallon pool. That may coincide with your issue but needs to be confirmed.