Left to itself, the surest way to compromise the integrity of brick is to allow algae to build up. Since brick is porous, over time algae that is growing in the pores will expand, breaking the binds and disintegrating the brick. Thankfully, with a little bit of work, you can keep your brick algae free and maintain it for years to come.
Mix water and vinegar in a bucket to create a cleaning solution. While some might recommend bleach, you run the risk that a neighbourhood pet might ingest it. Vinegar won't harm any animals, but it is effective at killing algae.
Put on durable gloves. While the vinegar solution isn't likely to hurt you if it gets on your skin (as bleach would), it's easy to scrape a knuckle when washing brick.
Scrub the brick. Dip your scrub brush into the cleaning solution and use the brush to scrub away the algae. Use a ladder if you need extra height to reach algae above your reach.
Rinse the brick. Using a garden hose and spray nozzle, rinse the area. Repeat the process as necessary to preserve the longevity of your brick.
If you choose to use bleach rather than vinegar, be sure to rinse the surrounding area especially well.
Always be careful when using a ladder.