This article is from the Beginning Fishkeeping FAQ, by Thomas Narten with numerous contributions by others.
For a 10-20g tank, once it is set up, expect to spend about 30 minutes
every other week doing partial water changes, cleaning the tank, etc.
If this is too much time for you, DON'T GET INTO THIS HOBBY! You will
also spend a few minutes once or twice a day feeding your fish,
turning the lights on and off, etc. Warning: many people spend much
more time than this simply looking at their tank and its inhabitants.
Of course, that is the whole point. :-)
Be prepared to spend several hours researching the hobby before you
make your first purchase. The more time you spend BEFORE you actually
get the tank, the smoother things will go. Go to several pet stores to
find one that looks like a reputable place. Visit them again several
more times. Get some beginner books. Read this beginner FAQ several
times.
Most people who get frustrated with fish tanks made mistakes that
could have been easily avoided. The way to avoid mistakes is to learn
the basics (e.g., the nitrogen cycle) BEFORE you put fish in your
tank. There are few things more upsetting than frantically reading the
FAQ for the first time, while three feet away your beloved fish are
dying. Remember: most aquarium problems are easy to prevent, but hard
to deal with after the fact.
 
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