Sign of fish tank needing base to be changed? (8)

I believe the answer is:

aquarius

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'sign' is the definition.
(I know that Aquarius is a sign)

I don't understand how the remainder of the clue works.

(Other definitions for aquarius that I've seen before include "Eleventh sign of the Zodiac" , "Sign of the zodiac, the water-bearers" , "The Water Bearer" , "Star sign" , "The Water-carrier, 11th sign of the Zodiac" .)

I've seen this clue in The Telegraph.

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