Dying (?) fish

Have a red and white comet, it appears to be on its last legs, lying at
bottom of tank,only swimming when it has too . It was brought home from
the pet shop about a year ago, is there anything I can do to put some
zing back into it? As a year seems a long time for a goldfish but
people have been telling stories of when they were a kid they had a
goldfish for 5 years.
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This post contains no hidden meanings, no implications and certainly no
hidden agendas
so it should be taken at face value. The wrong words may be used this
is due to my limitations with the English language .