Acacia is naturally antibacterial. Dark spots usually come from moisture building up when the board isn't protected with oil or wax, or is left wet.
- Scrub the spots with a paste of baking soda and water, or coarse salt and lemon, using a soft brush.
- For stubborn spots, wipe with white vinegar mixed 1:1 with water.
- If they persist, sand lightly with fine sandpaper.
- Dry completely and recondition with a food-grade oil or beeswax.
From then on, dry the board right away and store it on its edge.