Oxygenated bleach is an environmentally safer alternative to chlorine bleach, and it will remove unsightly stains and accumulated grime from your patio. Chlorine removes stains, but it will also kill surrounding plant life. Diluted oxygen bleach will not kill your grass, and it is effective at removing mold and algae that grow in damp areas. The bleach should be dissolved in warm water, according to the manufacturer's directions, and poured onto the patio. The chemical can be worked into the patio with a scrub brush or a long-handled corn broom to loosen debris. The patio should be rinsed thoroughly after cleaning.
Hydrochloric acid cleans brick and rough concrete, but it is not safe for smoothly finished concrete--it will etch the surface. It is a dangerous chemical and is not for everyday cleaning or maintenance. However, hydrochloric acid is especially effective at removing water and metal stains. It is available as the chemical only, or in prepared mixtures specifically for cleaning brick. When using it, you should wear protective eyewear, gloves and clothing, and protect the surrounding area's vegetation. The chemical can be applied to the patio with a brush or broom, then allowed to soak in and lighten stains. After stains have lightened, the area should be rinsed thoroughly. A second cleaning with a mild detergent will remove any residue.
Oxalic acid can be found in some household scouring powders. Oxalic acid is effective for general cleaning of concrete, but it works especially well on rust stains. Because scouring powder is the most common product containing oxalic acid, use it as you would any product of this kind. The patio surface should be hosed down, then sprinkled with the powder. Use a scrub brush or broom to work in the product, letting the powder stay on the patio for awhile to lighten the stains. For stubborn stains, use a little more powder and scrubbing effort. The patio should be thoroughly rinsed after cleaning.