fighter fish

I would change about a third of the water, once a week.

Do you ever need to change the whole thing to remove accumulated sediment?

with one solo fish, rarely would the need arise. (they don't live very long as a rule, anyway)

I would vacuum the sediment out rather than dumping all the water at once, if possible.

depends on how small is small...

Oh. I won't even think of what little household chore inspired the question.