I have been having the dreaded 91 error code at times, saying that there is a low salt level. I put in 3 bags of 40 pound salt and I still get it. This is on a 12x24 sized pool. I followed some tips and pulled the salt generator plate out and put it in muriatic acid for a few minutes, this plate looked spotless but I did it anyway, I also did this with another part that I was able to un thread from the unit. It goes from the intake side and is located right before the control panel box of the unit. I'm assuming this is the ECO but I'm not sure.
