I had tetra but i had to give them back because my water was too alkaline for them i didnt want any harm to come to them so i gave them back after only 3 weeks of having them, they did look noticably stressed and didnt eat to much, i may take some back in the future when i have bought an RO water unit
i have never had problems keeping guppys with tetra of any kind.but i have managed to keep some fish together that people say cant stand each other.(never had any trouble atall)