Be it further enacted, That the council shall appoint each year a board of equalization, consisting of three persons who are property owners and qualified of the city. The board of equalization may increase assessments made, and may add assessments omitted, by the city assessor on its own motion, after notice and hearing as provided in this article, but it may decrease individual assessments or strike erroneous assessments from the assessment roll only on appeals from interested parties. The board may increase or decrease the assessment of all property or of any class of property by a uniform percentage, in which case the requirement of notice and hearing shall not apply but a notice of such blanket increase or decrease shall be inserted once in the official city newspaper. The members of the board may receive such compensation on a per diem basis for each day of duty as may be provided by ordinance.