The actual salt level in the pool should always be tested first so that you know what the generator SHOULD be reading. 2100 ppm salinity is very low for these systems. They won't generate chlorine at this level. So is 2900, although the system may read ok and still generate. So either the salt in the pool is low, or the board in the system is going bad. When you calibrate, it should start at a much HIGHER number than the actual salt level and count backward until it reaches the desired level. Sometimes the desired level is a little higher, and it won't count back any further. That's fine, leave it. It will fluctuate a little, just recalibrate it from time to time. If there's too much chlorine, just back off of the output level; some even run at the minimum of 5% output.