The frequency of replacing bass strings varies from one player to another. There are cases when replacing them is compulsory like when they’re broken and thus useless and then there are cases when they just no longer provide players with the tone they want. Also, it depends on how often you play and how much you’re willing to spend on bass strings.
Sweat and dirt accumulate in the winding and this makes the strings sound dull. Cleaning them might help gain some of their bright tone back. However, when cleaning won’t do, replacement is required. There are a few signs to let you know when that moment has arrived.
If the strings no longer hold the tune as they used to, they produce a muffled or dull sound, they are discolored or have dark and rust spots, or they start to unravel, it’s time to get a new set of strings.