In Australia we get the el cheapo Pentair ECO-CHLOR this has a clear poly carbonate housing the electrode plates , mine after 3 months of use has gone opaque .
At first I thought it was calcium build up but when I removed it the plates and the surface of the housing was free of scale , i wiped the inside of the housing with my finger and bo residue came off . So it is the actual plastic which has change from clear to opaque .
The pool has 6000ppm of salt chlorine and acid/alkalinity have been fine and water temperature has been around 28deg Celsius with solar .
From what I have seen polycarbonate changes color with heat and or stress .
Any thoughts ?