Always ensure the pH is lowered first when you have Algae in the pool then increase the chlorine to 10ppm.

If you have persistent Algae problems you should check your pool for phosphates, algae feed on phosphates and if you have a good supply you will also get a good crop of Algae.
If you have too much phosphate use 'starver' to get rid of it.

Regards, Dave

Dave, its nice to have you here, but you do realise some of these posts are 8 months old???

Thanks Mitzyboy for the pointer,

I did note the age of the posts but warmer weather is coming and it will all soon be relevant again, some additional awareness is needed to be added for guidance.

Pool chemicals and awareness is very much missed and with recent health studied individual pool owners and proffessional pool maintainers need to have a much better awareness of the long term effects of poorly maintained chemical balance in the majority of pools.
This is not confined to Spain it is also from studies been found to be similar in the USA.
Public pols are rigerously controlled in Spain but it is not possible in the general to test private pools by the local health authority.

Some developments have a third party verification scheme which goes someway to ensuring better control, but in the end it is up to the pool owner to carryout their own checks to ensure the safety of everyone using their pool.

Regards, Dave