why do i have this awful black gunk in my toilet?

sideboom

New member
up until about November last year we had no problems keeping our toilets clean.but it has become a weekly task of cleaning it.(i thought at first it may be the round blue tablets we drop in the toilet tank staining it!)

could it be a water balance problem that comes from the city water?would appreciate to hear some reliable clues to this mystery on my hands.thanks!
 
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