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Having a look at your backlink profile, you lost alot of links around that time, but not referring domains.  I wonder if you deleted a sitewide backlink somehow.  These can give boosts of rankings for a few weeks, but will most likely give you a penalty at some point. You have quite a few other sitewide backlinks, but they are not that bad (33-40 links each) except pcdynamiceng.com which has 162 according to ahrefs.. I have see alot worse though, so cannot say if this is your problem. Another thing is the time of year... at the end of the summer people may not look for as many holidays etc.  Have you got metrics going back to last year to compare?.  This may not be relevant, but new sites get a nice boost for the first month or so as Google tries to ascertain whether they are popular \ useful etc.  It could be that this boost has simply faded away (I notice the site has copyright 2013). All I would recommend at this time, is focus on good quality content and spread that around on your social channels etc.  I would also review all sitewide backlinks, and try to replace those with relevant homepage backlink or editorial backlink.

One of our sites dropped 3 points for DA at the last Mozscape index so you are not alone. And this occurred at at time when our search traffic has been growing considerably and we are performing better for the majority of our keywords than we have for some time. For this reason I'm not unduly worried and considering it just to be a fluctuation which will probably improve in due course. In fact, having looked at our competitors which I've been tracking for comparison, I've also seen that all of them have also experienced a similar fall in this latest index update.

Hello, You have 3 actions you should take at the same time: 1. Build new high quality links 2. Reach out to the webmasters of those sites and ask for link remval 3. Use the disavow tool for the links that are not removed to avoid being hit by a Google penalty. Actually, those low quality links can trigger a penguin penalty if they abuse the use of 1 unique anchor text or they can even trigger the unnatural link penalty if the number becomes really important and your site gets a manual review by Google riders. Hope it can help. If you need further assistance, feel free to ask. Regards,

There's a smaller list in the Google doc mentioned in this post - http://moz.com/blog/web-directory-submission-danger 

Thank you Tom, I will have a look at the rel=canonical tag, doing things the google way always helps

I think that the answer to this question has nothing to do with the PA or DA of either site.  Exchanging links is not a bad thing.  It can actually be a good way to get links if you do it correctly. To answer your question, think of the following: -Are your sites closely related? -Would it make sense to have links to each other even if search engines didn't exist (i.e. would it benefit both sites' readers?) -Does his site consist of good material or is it all a mashup of low quality blog posts from other sites who are trying to get a link? My guess is that in this case you will find that the answer to whether or not you should do this is no.  But this may not be the case every time. I'll give you an example.  We have a real estate site.  I have a colleague with a home staging site.  His site is new and has low PA/DA.  My site has really good PA/DA.  I found a page on my site where it made sense to link out to a home stager.  In return, he allowed me to write a blog post for his site.  The blog post was a helpful one that his readers will benefit from.  Google is not going to get upset at a link exchange like that.  However, if you are doing this over and over and over again then it can start to look like a link scheme.