Hi, below is a copy of the message I sent earlier.
Hi
I am not a expert but i don't know how many males you have or how many females, we had the opposite effect, we had 2 males and one died which left one male and two females, the male went very depressed he just stayed at the back of the tank and I thought we were going to loose him (He's called Colin) - however we got another male and 3 more females and they are all so happy together and we even have a pregnant one. These Mollies aren't in the same tank as the tetras we have 2 tanks, we even tried moving the tetra in the other tank but he was just the same. We are going to try and give our tetra back to the pet shop if he will take it and I would either increase your mollies if you have the capacity (no guarantees though it will work) or like you said take him back because if your not happy and your fish aren't happy then it spoils the effect that aquariums are supposed to have on you. We got our aquariums to love them and enjoy watching them but we are now are at our wits end with this Tetra. He even takes over at feeding time
Please let me know how you get on.