My first tank was a 10g9possibly 20g) c. 1980. I was young, and made a lot of mistakes. I probably killed a dozen fish my first year, until I figured a few things out. By the time I joined the military c. 1985, I had 3 or 4 tanks up and running, but was still doing everything wrong by today's standards (air pump filters only, no heaters, wrong mix of fish, infrequent maintenance schedule, over-stocking, etc, etc), and it's only through dumb luck that I didn't murder all my fish. After a 10 year hiatus for the military, college, and kids, I started again in the mid 90s, and boy, had things changed. And they keep changing, even today. And, I still make mistakes, but luckily I haven't had any mass destruction of fish in several years.