Petroleum, a fossil fuel, supplies more energy to the world today than any other source. The United States is the world's leading consumer of petroleum; in 1994, Americans used 7,587,000 barrels of oil per day.
Frequently test for ammonia and nitrite (you want both to measure zero). A pH test is also handy to ensure your goldfish's water is not too alkaline or acidic. This can be purchased at any pet store. Do not modify the fish's water, however, unless it is significantly different from neutral.
I like the mosquito fish since they, well duh!, keep the mosquito larvae out of the pond, but if they are too much of a nuisance I will have to get rid of a lot more! The water parameters are all fine, and the goldfish behave normally (swimming around) except when I feed them.