When you say, "Some GT's", how many do you mean? Growing out four or five until you get the best is fine. But keeping that many as adults in a 135 won't work. A pair would be ok but two males would fight. The dominant one will beat the other one. some people have very aggressive GTs but for the most part they don't seem that aggressive to me. They will do fine with other large cichlids that don't attack them but will defend themselves if need be. Some of the ones that are commonly found in pet stores can be sickly, not always but quite often enough for them to have a reputation for it. Try to get yours from a good breeder/supplier to limit the chances of you having to constantly nurse a GT to health. Feed them a quality pellet, green peas, and other vegetables to keep them in good health.