Cleaning indian sandstone

I have an indian sandstone patio which is going green have power hosed it and this has removed the majority of it but on the lighter stone some are still green how do i remove this and how do i stop it coming back.

I am actually wondering the exact same thing The sandstone is green and black in places from moss etc. I am hoping to power wash it one of the weekends.

Does the power washing not remove all of the sand though? Did you have to brush more sand into it?

Thanks.

I grouted using a special mix i got from the guy i bought the stone from it sets in about ten minutes harder than concrete can be hosed no problem.

My guy just used sand...so guess if I power wash it I'll need to resand it??

Have you tried moss killer on the sandstone? Dunno but it might work?