Neal
Live life, don't let it live you!
Yesterday I bought some new accesories for my tank, and I bought two tetra neons and an albino bristlenose pleco, and put them in with my betta that I have had for about a month. When I woke up this morning I notice nothing was swimming around, then I notice two dead neons floating around, and then I seen my betta hiding behind my heater, and I couldn't find my pleco, I eventualy moved my heater and seen the pleco and all my fish had died. Do you think it was the betta or something to do with the water? (I'm quite new to keeping fish, so I don't know much) and why do you think it would have killed all of the fish? The pleco was only a baby and it stayed behind the heater so i'm wondering how it found it in the dark...
Are you sure the tank is cycled? What are your water stats? That betta is probably much more hardier than the rest of the fish are. Although little neons probably don't have a change with bettas.