Take a look at this post on The Pool Forum that describes a situation where the SWG cell won't output chlorine above a 1000 ppb phosphate level. Any ideas what is going on here? Is it just that the FC/CYA ratio is too low so the chlorine is getting used up fighting algae? I'll ask about that in the thread.
[EDIT] As you can see from later posts in that thread, the problem appeared to be too much algae growth that was consuming the chlorine from the SWG faster than it could be produced. Though lowering the phosphate level appeared to solve the problem, anything that would reduce algae growth would have worked including use of an algaecide (PolyQuat 60) or shocking with chlorine and then maintaining a sufficient chlorine level. The CYA level was also low so more chlorine would get broken down from sunlight as well. [END-EDIT]
Richard
[EDIT] As you can see from later posts in that thread, the problem appeared to be too much algae growth that was consuming the chlorine from the SWG faster than it could be produced. Though lowering the phosphate level appeared to solve the problem, anything that would reduce algae growth would have worked including use of an algaecide (PolyQuat 60) or shocking with chlorine and then maintaining a sufficient chlorine level. The CYA level was also low so more chlorine would get broken down from sunlight as well. [END-EDIT]
Richard