So, using your method of calculating the leak amount based on salt loss, I've updated the calculations. Pool volume is 23x13xx5x7.5 = 11,200 gals. Salt requirement for that volume at 3400ppm is 312lbs or about 8 bags (using pentair salinity calculator). So that's .028 lbs per gallon. I'm losing 20 gals/day or 7300 gals/year. Let's say 1300 of that is evaporation. That leaves us with 6000 gals loss/year x .028 (lbs salt) or 168 lbs, requiring four 40lb bags salt per year. This is less than what I seem to be requiring per year. This confirms your result above. I have not kept exact bag counts on salt use but I'm certain it's more than 4/year. My pool requires at least 4 when I open up in spring. Despite these irregularities, the salt loss is pointing to a leak.