After a decade-long study by a Mentor at my forum (RTR), he has concluded F8s do best in low-end BW SG of 1.005. His lived up to 18+ years, as singletons in that SG.
I had 2 live over 5 years in a 125 with cichlids and they held thier own, point though is I only added the carton salt now and then to the tank, I only lost them because of a tank crash do to filter fails.fun little guys though.