Dear John,
A most excellent reply, I am most grateful for all your expertise and er, yes I have a few questions.
To save you from them though, my understanding is that I should stick with H2O2 whilst I have guests; to avoid a green changeover between H2O2 and Chlorine, not with standing the fact there is too much Stabiliser and emptying 50 % and refilling is not an option so a changeover could not not be easily achieved.
If I continue with H2O2 level should be at 30-50 ppm.
For for a 75m3 pool, to raise the level would be 75ml water per ppm of H2O2? so to go from 25ppm to 50ppm I would require 25 x 75ml of H2O2? = 1.875 ltrs of H2O2. is my maths rubbish - i think it might be!
I thoroughly enjoyed your reply and am rereading it!
Best wishes,