Help with Sulfates category 

Hello, I don't know if you are the appropriate person to help with this, but I ask anyway. Plase take a look to the sulfates category, it shows a lot of fluorides, compounds that do not belong to that category. The problem is that none of the fluoride articles indicates that it belongs to the sulfate categories; in other words there are no links within those articles (as fas as I can see) to the sulfate category. Neither there is any link in the sulfate category page to any of those fluorides. How can we fix that, is it a bug in Wikipedia? Sorry, but I'm still not familiar with categories.
Best regards, I appreciate your help.