how to remove algae from exterior wall - and keep it off

[purplelilah]

hi all, my house is made of a cream coloured brick and on the front of the house there is green algae which looks awful. I think it comes from the fact it has a flat roof above it even though this is a new roof. Also part comes from a metal wondowsill. It was jetwashed in summer but has all come back

A friend suggested cleaning with a water/bleach mix then using a brick sealent to stop it reoccuring. Just seeing if people agree, also i read a couple things in the net that some brick sealant can create more damp and peel off. Any idea?
thanks

 

[foxhole]

A sealant will have no effect on it.