goldfish tank to tropical

Question
I had a loved goldfish for a long time in a 10 gallon tank(I don't know which:/).  I finally decided to add another and both died within a couple days:(  The new goldfish may have brought a sickness from the shop, I'm not sure.  I would like to switch my tank over to a heated tropical tank for a few tropical fish.  Should I empty and clean my tank and start from scratch, or should I do a 40% water change and get the levels even?  There is virtually no algae in the tank, it is very clean...  Just probably goldfish gunk under the rocks and whatever it was that killed my little guy.

Answer
Hi Kimba,
Sorry to hear you lost your goldfish. Maybe it was a sickness or something just went wrong internally. We can never know.

I would drain the tank down and gravel vacuum it very well. Then refill with dechlorinated water immediately. You want to preserve the beneficial bacteria that are living in your gravel bed and filter so don't let it dry out. I wouldn't do a big scrub down or clean out. A water change draining down to the gravel will do.

Let the tank run for several days with the filter and heater going and then decide whether you want to fishless cycle it or cycle it with fish.

You can read more about that here in this simple article.
http://www.firsttankguide.net/cycle.php

Fishless cycling is a humane alternative to using live fish-
http://www.aquatic-hobbyist.com/profiles/misc/fishlesscycling.html

Best of luck and I hope this helps!
Karen~