Hi there- we have a 150 gallon tank with 1 red devil or midas I'm not sure which is about 6 inches long and 3 tall. She's about 7 or 8 yrs old now. She had tank mates (a jack dempsy & a convict) when she was in a 30 gallon and of course she killed them. She's been in this 150 gallon for 3-4...