Not a strong clue for a mixture lacking strength (4,8)

I believe the answer is:

weak solution

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'not a strong clue' is the definition.
I can't judge whether this defines the answer.

'a mixture lacking strength' is the wordplay.
I cannot really see how this works, but
'mixture' could be 'solution' (solution is a kind of mixture) and 'solution' is present in the answer.
'lacking strength' could be 'weak' (I've seen this before) and 'weak' is found in the answer.
No letters remain.
This explanation may well be incorrect...

'for' acts as a link.

Can you help me to learn more?

I've seen this clue in The Globe and Mail.

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