I had the same issue with my Goldline Salt Cell. It was reading way low. It said 2000 ppm and when I had the water tested (at 3 different stores) it was 4500 - 4700 ppm. The cell was 5 years old and I was informed by Goldline that it was probably failing. I took it into Leslies and they tested it and it failed. So, I bought a new one. Now for the new set of problems.
Our pool (installed by the previous home owners) has the equipment about 35 feet from the control panel. The salt cells only come with a 15 or 25 foot cord. When the original cell was installed, they spliced the cord and lengthened it with some Cat5 cable. It worked fine for 5+ years. I bought a new cell and spliced it into the old Cat5 that remained from the old cell. The control panel wouldn't recognize the cell! I thought I just purchased a new cell that wasn't good, spliced the cable and now couldn't return it. So, I spliced the original 15' of cable back together and headed to Leslies to have it tested. It passed just fine. So, I went home and spliced it again using new Cat5 wire that I purchased. The cell is reading low again (2500 this time). At this point, I thought the board was bad. I called out a pool tech to check it out. He said the board was fine and he suggested that my length of Cat5 cable could be too long and is messing the reading (too much resistance on the line?). I am not an electrician by any means and don't know if that might be the case or not. I shorted the Cat5 length by 10 feet and it now reads 4400.
I have been messing with this for almost 3 weeks. I had to put a floating chlorine dispenser in the pool temporarily to try and keep the levels right. And, a couple of times I had to scrub the pool as algae started to form (which I've never had to do in 3 years). The people at Leslies think I'm crazy because I've been in there 3 times to test my Frankenstein Salt Cells with their splices hanging out. I am thrilled to have it working and had to tell someone the story who might get it. My wife doesn't understand it at all. Also, I learned a lot about pool maintenance/care during this time reading these forums - thanks.