I never had a problem keeping my group with other fish. Mainly with Chinese algae eaters and jewel cichlids. Kept probably five CAE and ten jewels along with six rbp in a 6x2x2 when the rbp were probably 9”.
My previous attempt ended with the convict cichlids I was trying, killing my five 4” rbp.
You managed to keep six adult red belly piranhas with Chinese algae eaters and jewel cichlids? You must be the fish whisperer or something because that won't work 99% of the time. More like 99.9% of the time. The piranha simply interpret those fish as food.
AND you had convict cichlids which killed five medium sized red belly piranha? Were you adding steroids to their food or what? ?
Crazy stuff going on in your tanks. Please take video next time stuff like this happens because I'd love to see.