This is what we use for hydra.nixos.org.
MGHUN7RDWRURBAJ6RQZ6DKVAGIXIBZIS54RAJVSTSQEKDPOXM2GQC
LYO7KK3JD3PBYBWSLAO6UKEPVCBUGZ2PWDBPDCY3W7TH3HFOL7TAC
RWNXH3H26EQHKJNMP4DUJCJKUYQBMV347234ZLE26SIFTVLSUWXQC
postgresql95
postgresql_11
services.postgresql.package = pkgs.postgresql95;
services.postgresql.package = pkgs.postgresql_11;