My son has had his 10 gallon aquarium for 4 years and the goldfish we had in it just died a month ago. The 3 yr old goldfish my youngest son has in his aquarium are still going strong. I knew they would eventually die, if nothing else due to the fact that goldfish never stop growing at least internally, eventually they outgrow their space and die.
I ran 48 and 60 gallon aquariums for years and had very few problems. The best fish I had were Oscars, I bought them when they were about 2" long and we had them for about 4 years, we had to get rid of the aquarium and the fish were were about 8inches long and weigh in just shy of a pound.
I have always wanted to try a saltwater aquarium, I would make sure it is as large as possible(easier to care for) and have it up and running for a good month before adding the first fish, It will most likely die, then add another, if it lives add maybe 2 and see how it goes......
