I have a victorian 'Grotto' ( a style of conservatory with walls made to
look like the inside of a cave but with multitudinous pockets of soil in the
rocks for planting puroses)

There was some difficulty replacing the glass roof with the result that it
was open to the elemnts for some considerable time and the rock- which I
suspect to be Tuffa- has become much covered with moss and lichens.

I have removed most of the plants and the soil but would like to know what
would be best way to kill the green growths on the rocks to restore their
colour back to the origionalwhite/yellow and allow replanting (with fresh
soil in the pockets)..
I have been told that some chemicals may prohibit replanting for a very long
time.

Any suggestions greatfully received

Regards