In a multifamily development under management of a single landlord, all tenants of rented low- and moderate-income units shall be required to give proof of continued income qualification the first and each subsequent anniversary date of taking occupancy. A tenant shall cease to remain qualified if the total household income exceeds 125% of the moderate-income limit. Any tenant household not remaining so qualified on the first or subsequent anniversary date of taking occupancy shall be required to vacate the rented unit upon nine months' written notice if there is a qualified applicant available for such unit; provided, however, that a household that ceases to meet the qualifications as a low-income household, but does meet the qualifications as a moderate- income household, may continue to occupy the unit, and the next unit to become available which is owned by the same owner as the unit changing from low- to moderate-income occupancy shall be rented to a low-income household. Upon the issuance of the written notice to vacate, the limitation of rental charges as set forth in this article shall cease to apply, and, until the subject unit is vacated, the owner shall be entitled to an increase in rent, provided that the increase does not exceed 30% of the amount by which the tenant's income exceeds the current maximum income limitation for a moderate-income household. In the implementation of this subsection income limitations shall be as adjusted for household size.