Swimming pools blog

Hello,
I’m new to the group and if this is an old topic if someone could e-
mail me the thread that would be great. I bought a house with a salt
water pool this summer and I think I understand all the systems now
except for my chlorinator. Here is how it behaves:
* My water analysis shows the water is balanced including the
stabilizer
* My salt readout is between 3.0 and 3.5 as recommended
* My chlorine levels seem stable and adequate for many days
* Over the course of 2-3 days my chlorine level drops to zero
* Salt is being consumed. I’ve added 120 lbs since July
I then throw up my hands and throw some chlorine tabs in the water.
I’ve done the acid bath cell cleaning per the manual (the deposits
weren’t bad.) and yes, I set the production level at 100%. All other
readouts are fine.

The unit is four years old. How often should the cells be replaced?
Any other advice would be appreciated.
Puzzled … -Rob