I have had two calico fantail goldfish for about seven months, and they have always been pretty healthy.

After buying a bigger tank, I decided to get another fantail. This one, however, was really small - less than half the size of the other two. It seemed really shy, and would always hide under plants and decorations I had in the tank. The other two fish mostly ignored it.

It had a hard time getting food because the other two would get to it first, so sometimes I would separate him to feed him.

After having the new fish for about a week, it died.

The water quality and everything is fine... but I'm still not exactly sure why he died. I'm assuming it was the stress of being put with two bigger fish, and maybe because he couldn't get enough food? If anyone has any suggestions I would appreciate it.

Thanks in advance for your responses.

I forgot to mention that his death was a surprise to me. The whole time I had him he seemed healthy, and I saw no sign of diseases.

Another question - the two other goldfish are fine, but should I do a partial/full water change anyway?

Wallflower, If the others were leaving the small one alone, chances are he didn't die from stress of them. There may have been a problem with him, or the difference in the water. (without knowing the water on your tank and theirs is hard to say).

I would do a water change, and if you see anything going on with the other 2 post in the diagnosis section.

Sorry the little one died. Normally a size difference of half isn't a big deal.