(d) If on July 17, 1985 the rent being charged exceeds the allowable rent ceiling, that rent shall be reduced to the allowable rent ceiling effective the next date that the rent is due. This subsection shall not apply to any rent administratively approved under the Rental Accommodations Act of 1975, the Rental Housing Act of 1977, or the Rental Housing Act of 1980, or any rent increase authorized by a court of competent jurisdiction. The housing provider shall notify the tenant in writing of any decrease required under this chapter before the effective date of the decrease.