How to get rid of presumably limescale from your pool?

Be careful with anti calc, early formulations were often phosphate based and phosphates are like caffine to algae etc. Later versions tend to be based around Ethylenediaminetetraacetic acid (EDTA) which is a metal sequesterant but can help with water hardness. EDTA is slowly used up by chlorine breaking it down so requires frequent topping up. As you said Roger better to top up by harvesting the rain water, that will be dirty until filtered and will use more chlorine initally but it is a solution.

I too live in a hard water area but do not suffer from scale, When the pool was installed (six years ago) the pool man added a product called anti-calc (?) to the pool followed by the other chemicals to give the correct Ph. Its only during the high summer that we need to add any water at all, during the winter its usually a case that the pool overflows with lovely soft rain water. If you are having problems with high evaporation then you need to use a cover.

Welcome Terry,

It is all a question of water balance. France is a big area and some of it has very hard water like yours and a somewhat like mine. What you really don't want to be doing is changing the water every year for fresh water with yet more hardness to deposit. Sorry, it's better to treat the water you have and maintain that at the correct levels. That requires testing and accurate testing. To reduce the hardness you could filter through a reverse osmosis filter but you would need a big one! You could use a water softner which is full of salt which softens via and ion exchange so sodium replaces the calcium (that is the scale) similar to why some report salt water chlorine pools as feeling softer. Or counter the hardness with an increase in the acid level. That would reduce the pH which would then need to be raised without the addition of chemicals or you'll end up where you started. Over a period of days you will then get the hardness lower and the pH stable at a point where the water is neither corrosive or scaling. At that point you want to keep that water in the pool for as long as you can and then maintenance will be so much easier and cheaper.

That is a simplified version but it is what needs to be done to balance the pool and we can look at the alcalinity levels too as in a tiled pool it is important to get the levels corrrect or the grout gets erroded over time as apposed to scale forming.