sometimes clean water and a stiff brush will remove it.
if that does'nt work, just go into travis perkins or b&Q etc and buy any efflorescence remover/salt neutraliser..once again, brush it onto the area with a stiff brush.
Just finished a garden that had nearly 3,000 Red Leicesters and had a bit of efflorescence show up - gave it a quick application with brick acid and a brief jet washing sorted it.