I have some dark leaf stains on my patio from last year that just won’t go away. Should I just let it be, or do you recommend something to remove them? Perhaps bleach?
Eventually, the dark leaf stains will go away. Weather and ultraviolet sunlight will get to the stains, but it takes some time. Bleach can be effective with detergent.
If you want quicker action, try scrubbing with a strong solution of MEX. You will find MEX at the hardware store. It is a strong detergent specifically designed for concrete and masonry surfaces. Mix a strong solution in very hot water, then scrub with a stiff brush. Allow it to soak, then scrub repeating several times.
You could also use a cleaner that contains oxalic acid like Zud, wood bleach or a deck cleaner. This will remove the stains, but may also lighten the concrete surface color. You may need to clean the whole patio once you start with an oxalic acid cleaner.