Needing Advice on Dying fish

Thanks for your prompt response.  In fact, I did do a 25-30% water change as I was introducing the new fish.  I bought some more live plants and decided it would be easier to plant them with the water level down.  After returning home yesterday (from being out of town all weekend), I noticed 2 more of the new fish had also died.  In total, I had purchased 9 fish. Is this simply too many at once?  Did I overload my system?

Thanks again,

Jason