The honest answer: it depends on the pairing
Of the questions keepers ask about cohabitation, this is one of the few with a conditional yes. Common musk turtles are small, bottom-walking turtles that can sometimes share a tank with their own kind — but the outcome is decided by the sex and size of the pair and the room and structure you give them, not by any social need. Musk turtles do not seek companionship; at best, a well-chosen pair tolerates each other so completely that they live parallel lives in the same water.
Pairings that work and pairings that fight
Two females of similar size are the most reliable combination and often coexist for years with no more drama than an occasional contest for the best basking spot. Two adult males are the worst bet: males are territorial, and persistent chasing, biting at legs and tail, and one turtle being driven from food and basking areas are common outcomes. A male with a female brings a different problem — relentless courtship attention that stresses the female, suppresses her feeding, and can injure her over time. Size mismatch undermines any pairing, because the larger turtle claims resources and the smaller one's world quietly shrinks. Whatever the combination, be ready with a second setup; a pairing that works is a pairing you are still prepared to separate.
Space and structure make tolerance possible
A shared musk turtle tank needs to be sized for two territories, not one turtle twice: a long footprint with visual barriers, plants or wood that break sightlines, more than one hiding place, and basking and feeding opportunities at both ends so neither turtle must cross the other's ground to eat or warm up. Feed the pair at opposite ends and watch the smaller or shyer turtle actually eat — musk turtles spend much of their time on the bottom, and a bullied individual can be outcompeted at the substrate level where you are least likely to notice. Water quality also doubles its workload with two animals, so filtration and water changes must be planned for two, not stretched from one.
Behaviour that means separate them now
Treat these as closing arguments: biting that breaks skin or targets the same turtle repeatedly, one turtle spending its days hidden and skipping meals, chasing that resumes after every separation break, or wounds around the legs, tail, or neck. Musk turtles also release their namesake musky defence when stressed, and a tank that regularly smells of it after disturbances is reporting a social problem. A short trial separation that transforms the shyer turtle's appetite and activity is the clearest verdict you will get — believe it, and keep them apart permanently.
Two turtles, honest records
Keepers who succeed with a pair treat them as two individuals sharing water: each turtle's appetite, basking time, and growth get noticed separately, and the spare tank stays available rather than sold. That individual attention is easier when the household shares notes instead of relying on whoever happened to feed last. KinsLe's Family Sharing shares each musk turtle's profile and care information with family who help, so a note about nipping or a missed meal follows the right turtle and everyone sees it.