DIAGNOSIS The pinkish biofilm is Serratia marcescens, a common airborne bacteria that thrives in damp, dark environments. It is not harmful in small amounts but indicates inadequate cleaning.
FIX Remove the reservoir by lifting it straight up from the base. Do not submerge the base. Clean the detached reservoir with a solution of 1 tablespoon of unscented bleach per gallon of warm water. Use a soft bottle brush to scrub all interior surfaces, especially the corners and the opening at the bottom. Rinse thoroughly with clean water until no bleach smell remains. Allow it to air-dry completely before reattaching.
IF THAT DIDN'T WORK For persistent stains or scale, use a solution of white vinegar and water (1:1 ratio). Fill the reservoir and let it soak for 15 minutes. Scrub and rinse thoroughly. Follow with the bleach solution to kill any remaining bacteria the vinegar did not address.
HEADS UP Never use abrasive scrubbers or steel wool on the reservoir. They will create micro-scratches that make it easier for biofilm to adhere and become more difficult to remove in the future.