Just to reiterate... I'm sure you get tired of seeing all the "you need to post numbers" and "you need to test" posts.
Your salt generator is adding chlorine (free chlorine) to your pool constantly when running, and that may be sufficient for your pool, or may be too much, or not enough. You seem to have something in the pool which the free chlorine is attacking, and forming chloramines or combined chlorine (CC), but there is no way to know the eco-system in your pool without some real numbers. Maybe all you need is some sun. Or maybe you have a serious problem lurking in your water.
Your pool may even have a significant algae bloom, and the constant addition of FC via the SWG could be *just* holding it in check. That would be using up virtually all the chlorine being generated - an equilibrium. Algae doesn't become visible, FC doesn't stay in the pool. An overnight loss test reveals this. If this is the case, then you should elevate the FC level to shock target, and hold it there until no further overnight loss occurs.
Your target levels will be determined by the CYA (stabilizer) level of your water.
Without knowing SOMETHING about your water chemistry, we can only offer guidelines and guesses. Get us some test results, and we can tell you pretty much exactly what you have and need.