bored w/ food...heather

You can rotate two food but IMO I would try the food alone to make sure it agrees with his belly first.   Then when you find two food then you can mix it up.   When I did food rotation I found three food Hanna could eat and liked.   I would buy one bag, then when it was gone buy the other kind and do it over again.  Mine stayed on a food for 6 months.  

If he is not eating shorter than 6 months my only issue with food rotation is that he is going to figure out if he does not eat you will give in an switch his food around.   Thats not good, thats the dog controlling you.   So I would make a chart of foods he likes and will eat, and then go from there.

How long has he been on Blue?  How are his poops?

I would finish up the bag of Blue - then here is some good info from Dog Food Analysis -

Do I have to change brands every time I change food?

No, not necessarily. Look at the ingredients in the different formulas made by your brand. What is different? If it is only the main meat ingredient, then you should change to a different brand when you change foods. If many of the ingredients, including the main meat, are different then there is no need to change brands if you don