No. Not in the traditional definition of the tropical tank. A tropical tank is a freshwater aquarium. Regal Tangs are saltwater fish and go in a saltwater tank (marine aquarium).
The gas tank on the 2012 Buick Regal holds 18.0 gal..
The gas tank on the 2004 Buick Regal holds 17 gal..
The gas tank on the 2003 Buick Regal holds 17 gal..
The gas tank on the 2014 Buick Regal holds 18.0 gal..
The gas tank on the 2002 Buick Regal holds 17.5 gal..
The gas tank on the 2013 Buick Regal holds 15.8 gal..
The gas tank on the 2011 Buick Regal holds 18.0 gal..
The gas tank on the 2001 Buick Regal holds 17.5 gal..
You can safely keep a shoal of neon tetras (tropical) in a 17 gallon tank
Rule of thumb is to not mix tropical fish and goldfish.
Use a tropical fish tank, preferably new. That way you know that it should not leak. Try to avoid using a tank that was used for something other than tropical fish. I prefer glass tanks over acrylic because they are less likely to mark or look dirty and they are easier to keep clean. Most aquarists will tell you to start off with a small tank and as you enjoy it more and more, you can opt a larger tank. When I started into tropical fish and as I bought larger tanks I used the smaller tank for breeding. Tropical fish tanks and supplies are available in most pet stores that sell tropical fish.
Its probably from the filter you are using, and probably from the natural fish oils.