Mold on below grade garage block walls
Get some hydrogen peroxide, dilute to 7% with water and spray or roll it on the blocks. Within 24 hours the mold is gone any that is still left reapply and that usually takes care of mold on concrete block sometimes a 3rd round then an occasional treatment keeps the concrete bright.
No chemical residue to worry about the hydrogen peroxide breaks back down into water and oxygen.
If you get strong hydrogen peroxide on your hair it will bleach it, gloves and glasses should be worn.
I purchase my hydrogen peroxide online at ?30% in gallons but I live in Oregon and some places have year round mold problems I kill mold prior to working with it because I don’t want to breathe it.
Just a note I am not sure how long it lasts but if not kept in a dark cool area it turns back to water after a few years so far mine gets used before that long as it is a great sanitizer with no bleach stink (learned that working in a hospital years back).