You'll need to get to the source of the problem. Mold thrives on moisture. It isn't really possible to give suggestions without knowing the cause of the trouble.
A couple of recs. Run A/C more. Run a dehumidifier (costs about 30-60 a month in elec.), add an exhaust fan for the basement (this does work, and is cheaper than dehum.)
Can't say much more, no chemicals will resolve this issue.
Post reasons, and we can provide solutions.
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