compatability-whos eating the tetras?

Question
Hi,
I have a fifty gallon tank. Established for about a year, there are 2 large gold fish and 1 pleco who is getting large also plus one cardinal tetra. Approx. five days ago, 5 sunburst platy and 5 serpae tetras were introduced to the tank. The following morning one of the new tetras was found with it's tail bitten off. It died shortly after. Two days later the cardinal tetra was found eaten except the head. One of the platys was also found dead for no apparent reason the day between the two tetra. I'd like to know if these fish should be compatible together or did I make a bad choice of fish mates? Thanks in advance for your help.
Valerie

Answer
Hi Valerie
Well, it's generally not recommended to mix goldies with tropical fish.  Unless you have one of the fancy varieties, most goldfish require a cooler water temperature, and goldfish are known to put out a bit more ammonia naturally.  And, it's hard for the other fish to compete for food.  But, as I mentioned, if they're a fancy variety, that's not necessarily the case.
But, my guess would be the goldfish are the ones causing the problems.  They will generally eat whatever can fit in it's mouth.  Usually I would say keep an eye on them to be sure they're not chewing on the fish AFTER they died, but the fact you saw one still alive with it's tail bitten off makes me think otherwise.  You'd probably be best off returning the tropical fish, or getting a separate tank for them, and leaving the goldies and the pleco alone in the 50 gallon.

Hope that helps, and good luck with them!

Christy