Why major difference in keyword positions?

[Rebeccazadeng]

Hi all,

For August month for the keyword "joomla templates" we were ranking in 8th position. The very next week I found that the keyword was not ranking inside the first 500 positions. Till now i am facing the same issue

Not only with joomla templates i have similar issue with couple of other keywords like Html templates, Oscommerce templates, Website templates membership, Html website templates etc. At the same time few keywords like Business Website Templates, Business Web Templates, Membership templates, Software Templates were ranking in the same top position and they have not dropped yet.

I am just wondering why this major difference. Because of this ranking difference we lost almost 60% of the visitors while comparing with august month traffic. Advance thanks for your replies.