HG Algae and Mould Remover 1L Algae Remover for Patios HG algae and mould remover is an effective algae remover. Overtime, algae and mould can build up on patios, walls, roofs, and all types of concrete outdoors. This effective algae cleaner makes your patio cleaner and your life easier. Read below to find out more about HG algae and mould remover. HG algae and mould remover is easy to use. You can remove mould and algae from your patio or other concrete in just 36 hours. When you apply this algae cleaner, it penetrates deep into the surface of the concrete. HG algae and mould remover not only works as a mould and algae remover. As well as removing algae and mould, it also protects your patio against algae building up again for months.