Two thoughts....
first, with that much return water going thru the water feature (I imagine it is a waterfall of some kind) you will probably have a lot of evaporation....but that should be concentrating your salt levels...not diluting it. What exactly is the water feature you have and is it a possible source of the leak. Other places to check for leaks are your skimmer and your light niches.

Second, it would be helpful if you could post a full set of test results for FC, TC, pH, Alk, Cal, CYA and Salt. If your cell is getting a lot of deposits it might mean that your Cal is very high. Also what is the surface of the pool (plaster, fiberglass, vinyl) and how many gallons?

BTW, low salt levels can cause a cell to die prematurely.