Lol, your ranchu that batch itself may not be good.
Maybe fish in fish farm is heavily drugged so they can never give
birth anymore, might be more or less the reason you ranchu
died.
Ranchu is in fresh water one, so ph should be around 7 to 8. Anyway
did you buy heater? Sometime you need to adjust the temperature to
the fish comfort especially when it is sick.
Did you put some dyed medicine inside to stablised the water and
heal the fish?
Anyway don't be sad lar... Maybe you can buy some new Ranchu, my
friend is selling, can sell you at discounted price if you want,
and he can provide better fish rearing stategy to you.
By the way, where u bury ur fish? Inside a big hole?? 
