I have been having trouble raising the FC level in my pool above 1.0 PPM.
I replace my Rainbow 320 chlorinator thinking there was something wrong with it. The new unit dissolves the chlorine just fine, but the levels never rise.
Warehouse Pool Supply (WPS) suggested testing the water and what we found on two different test over a three day period was this:
Free Chlorine -- 0.4 ppm
Total Chlorine -- 0.4 ppm
Combined Chlorine -- 0.0 ppm
pH -- 7.6
Hardness -- 275 ppm
Alkalinity -- 80 ppm
CYA -- 110 ppm
WPS stated that the CYA was "not bad", but could not tell me where all of my chlorine was going.
So I jumped on the web, found this site and others, and discovered that a CYA of 110 is a problem, and is only fixable by changing the water. So I did what I thought for sure would work well. I dropped the level in the pool by 20", and refilled it. I took a photo of my water meter before and after, and this is equivalent to about 6500 gallons. I refilled the pool with tap water. (BTW, the tap water tests at 4.5 ppm and ZERO CYA)
Went back to WPS, CYA is at 100, verified by my in-home test kit. I thoguht for sure a 1/4 change would make a bigger dent.
So now what, more water change?
Drain the pool completely and re-fill?