After 4 years of working with little need for cleaning, my intellichlor IC40 now requires frequent (about every 1-to-2 weeks) acid wash else it will not produce chlorine. The reason is pretty obvious, it builds up significant amount of minerals between the plates, near the top and bottom edges.
This photo shows the scale buildup view from top https://flic.kr/p/pa9cbU
and this one from bottom https://flic.kr/p/pa8Qu2
These two photos are after washing with acid: https://flic.kr/p/ppB29s and https://flic.kr/p/prCT5e
Note that the most central plates in the cell, where most buildup occurs, have been eaten away (best seen in photos after washing ).
Where do I start looking for the reason for this. Chemistry (my PH is fine I keep it 7.5-7.8)? Chlorinator (rotten cells)? Any help is welcome.