I have a steel frame pool which holds just under 5200 gallons. When I set the pool up I added 176 lbs (4 bags of pool salt) which was a bit under the 190lbs that the manual recommend. Everything has been great for 3 weeks then the other day the salt level light was flickering between low and Ok. The manual recommended to add 35lbs of salt for my size pool if the low light came on. I add the the salt and everything was fine however two days later the salt is reading low again. I have not added any water since filling the pool on June 1st. Is something else going on here? Could a dirty cell in the SWG cause a low reading as we have hard water from the city? I was under the impression that once the salt level was good at startup that I shouldn't have to add anymore? The SWG is a Bestway Flowclear Model 58215.