Anonymous posted an answer for this 3M Filtrete Ultra Allergen Air Filter (Purple Series) 12x36x1 Filtrete Purple Air Purifier:
"I am also experiencing this problem, as well as 2 other people that I found on google, so..."
Anonymous posted an answer for this 3M Filtrete Ultra Allergen Air Filter (Purple Series) 12x36x1 Filtrete Purple Air Purifier:
"my filtrete central air filters turn black after about a week"