Voters will choose City Councilman James D. Petrikin's replacement at the Nov. 3 general election.
Saying he suffered health problems, Petrikin resigned in May amid accusations he was living in Northern California, violating an election law that requires council members to live in the cities they represent.
The City Council on Tuesday opted to fill Petrikin's seat by election rather than appoint a replacement.
Candidates have from July 13 to Aug. 7 to file for the race; the filing period might be extended if any of the three council incumbents do not seek reelection. Seats held by Mayor Laurann Cook and council members John J. Collins and Guy Carrozzo are up for election this fall.
Petrikin's replacement will complete his term, which runs through 2000.
Also Tuesday, the council amended the city's massage ordinance to require stricter educational prerequisites, including passage of a national exam, before being able to gain a city operating license.
The law aims to weed out prostitutes posing as legitimate massage practitioners, officials said.
Fountain Valley needs the same tough restrictions as neighboring cities to prevent prostitutes from setting up shop, Police Chief Elvin G. Miali said.
Council members delayed until June 16 a vote on a proposal that would require massage therapists to submit to annual testing for sexually transmitted and other diseases.