I found the best way to troubleshoot spotting windows is:
1) Lick your thumb/finger and wipe the frame. If a chalky white deposit is left on your finger, no amount of cleaning will ever solve this as the UV light has destroyed the UPVC composition and it will always powder up and chalk... clean the following way:
ON A LOW FLOW RATE ! Clean all the frames first. Start from the top and work your way around the house only doing the top windows, just the frames only forget the glass for now. Once you have finished cleaning all the frames on the tops, go right back to where you started and do the bottoms the same way.
NEXT.....ON A LOW FLOW RATE, just clean the glass only, do not touch the frames, do not get the bristles on the frames, do not 'rinse' the window with gushes of water as you will wash chalky deposits back on the glass. JUST DO THE GLASS, slowly and on a low flow rate, continue all the way round the house as before doing tops first then go back to the beginning and do the bottoms.
This way you will end up with perfect results on bad windows..
Oh and make sure your water is...000 tds not 001 or 005 or 015!!!!!!!
ZERO ZERO ZERO is your HERO