I am really curious. I am assuming the male and female betta were in separate tanks. Is this correct? It is unusual to have six deaths in one day in separate tanks. If, as your LFS says, it was bad water, what was bad - the ammonia, nitrite or nitrate? A Nitrate reading of .25 hardly means a tank is cycled, but even if I am wrong, bettas are really pretty hardy fish so why would two of them die in separate tanks? Seems like some investigation would be necessary. As OC, says - Just my 2 cents worth.