How to deal with duplicate content properly?

I have two sites. One site has a specific focus and is the primary site. I have a second site I started on a different domain (but domain is older than the first domain), that carries the content of the primary site (all original content forums and information) along with additional content not carried on the primary site.

My goal, was to eventually phase over everything to the new domain, but didn't want to do that until the new site took off. I feel however, I have been given the duplicate content penalty a year after I did it. Almost the same day, both sites dropped rankings and traffic from Google dropped to 1/10th of what it was.

The sites need to be implemented the way they are now. I didn't start the new site for SE purposes or to get additional ad revenue. This is strictly for the site and the users.

If I go in and robots.txt (block) out the content on the secondary site, which duplicates the primary site, will that be sufficient to not be accused of duplicate content? Or just the fact it exists still hurt me?

 

yes, it's duplicated content and google will see this and will take the most trust domain as the original and ignore the second site in the search results.

you should create 301 domain forword from the old domain to the new domain that you want to be working with, these will also transfer your old domain pr