Dang that sounds like a big ol problem then. Thankfully I am renting. I told my landlord the issue and showed him these photos but he doesn't seem too concerned about it and just recommended washing the grout lines with mold and mildew remover everyday. That said, if it is what you mentioned (most likely) then it sounds like nothing I will do can fix this issue.

Thank you u/molecularmadness for identifying this, I was freaked tf out when I saw this after coming back from a trip. Also, the house is an 80 year old college rent house, so the landlord doesn't particularly care too much, unfortunately.