Is your CYA dropping also? It should be. If you are losing salt and CYA fast there are several things that could be going on.

First thing I would do is check for leaks if your salt and CYA is dropping much faster than it has in the past. Have you had to put in water more often then normal (The heavy rains you reported could be masking this.) A bucket test might be in order.

What kind of filter do you have? Filters that are backwashed will remove salt and CYA from the pool with every backwash. If you have such a filter are you backwashing more often?

Does your pool have an autofill device and and overflow drain. If the autofill is not shutting off then water can be going into the pool and draining out constantly. This would also lower salt and CYA levels.

How big is your pool?
It wold be very helpful if you would post info about your pool and equipment so we can get a grasp on what might be going on.
If you have a small pool then 80 lbs of salt is a lot but if your pool is 20k gallons or bigger it's not. In fact in a 20K pool 80 lbs of salt will only raise the salt by less than 500 ppm! (about 480). This is less than the precision that some SWG units can report salt levels!

Give us a bit more info and we will see what we can come up with.