Thanks Carl & Kalemvor,

I will follow your plan towards the end of the week, when I can be around.

1. Shocked with Cal Hypo 73%. Hope I can finally be ahead of this and keep it away.
2. Pool loses about 3-4 inches/week in summer depending upon dew point, and has done consistently. Loses a lot less in winter, even with pump running similar hours.
3. SWCG appears to be fine (clean), reports increased salt after being added, flashes if I put too much in. Chlorine levels appear to be fine unless the SWCG reports needs more salt. I followed builder's suggestion for salt, and only add when SWCG suggest salt levels are reducing.
4. Brushing isn't always easy - often away from home 14 hours/day, and lose light. so that is an area I need to work harder at.
5. Obtaining strips for salt - cynicism isn't pretty, but always good to be sure, thanks for links
6. Muriatic - OK leaving it on the shelf, I know how to take instruction

Cheers