Rich,
What WFP system are you using?
Are you using DI only, or R/O but feeding the water through the DI directly as you use it??
If everything you did was spotting then the water that was hitting the glass must have been contanimated in some way.
Set your water flow to exactly the same as on the day you were having problems, disconnect the hose from the brush, fill a glass with the water and check the TDS.
If TDS is high then the problem is probably at the DI end.
If the TDS is good then your brush may well be contanimated.
Is the brush of the flocked variety or the single filament type?
The flocked ones if they become comtanimated, because of their nature, can remain contanimated longer than the single filament ones.
If you wash out your brush, regardless of the solution used, make sue you rinse the brush out in first normal tap water and then in a bucket or two of pure.
If you can leave your brush in a bucket of pure water at 0.000 TDS and agitate & leave to soak for a little while, when you check the TDS of the water it should still be at 0.000 or as near as damn it
You could also make sure the settings are the same as when you were having problems and clean a couple of your own windows to see if they too spot up. ( prior to cleaning everything out of course!)
Good luck
Ian
