I would think in order for it to work you would have had to introduced them into the tank at the same time at a very young age, these two being the only clowns in the tank. I also think they would both have to be captive raised clowns, not wild caught. Once a clown has paired with ot's own species, I doubt it would pair with an outsider, especially a clown of another species. Personal experience for example; I have a female Convict (very prolific and will cross-breed with any CA/SA cichlid) who was paired up and reared fry with her mate on a regular basis. I introduced a replacement mate for her when her mate died, didn't work. She has killed off any CA/SA cichlid I have put in there for her, well any inhabitant I have tried to introduce period. I'd try to get another Tomato, a smaller one preferred. If you were to attempt another clown of a different species, atleast attempt something a little more similar, like a Cinnamon.