Two keywords of my website flactuating everyday

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I have a product website. I am targeting 16 keywords and 2 of them are not  
ranking constantly in google. I have analyzed my website properly and I am  
also not doing black hat seo for ranking in SERP. Please suggest me what I  
need to do to resolve this issue. My website's page url is http://thecandyl and these are my keywords:    
sixlets candy bulk
sixlets candy in bulk

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