Possible tankmates for my 30 gallon?

[Shnawp]

I currently have a 30 gallon tank with a filter, heater, plenty of (plastic) plants, and a sand x gravel combination floor. I have a black moor goldfish that's about 5 inches not including the tail, an opaline gourami, a peppered loach, a black kuhli loach, and a (very shy) molly.

The only fish I ever really get to see are the gourami and the goldfish, and I've been looking to get another mid-level swimming fish that's hopefully somewhat colorful and around the gourami's size. I understand if this isn't possible, but it would be preferred (in a perfect world).

I was thinking of possibly a rainbow shark, but I'm unsure if it will pick on the goldfish.
I was also considering maybe a few gold dust mollies to make my current molly a little less shy, or possibly a school of cardinal tetras.

Any suggestions or advice? Maybe some interesting potential fish that I may not be aware of? Thank you!

 

[Chrisplosion]

Well your mixing a goldfish which is a cold water fish with tropical fish which isn't really a good idea. Outside of that you could look into Ram Cichlids. You could have a pair of them or a male by its self.

 

[DIDYSIS]

Could always add a heater and turn the heat up a little in the tank. Unless you already have a heater. With a gold fish just warm the water slowly. But really you should either stay with cold water fish or tropical apart not together