Haze is throwing up now :-\ He used to be on Pedigree but I wanted to start using Iam's

I slowly tried transitioning the food.. but now he is throwing up... Whats do I do?!

Both of these are very low quality foods....I would choose a high quality food to switch him to.  Ratties often cannot tolerate the corn fillers in foods like Iams and Pedigree...or the preservatives, dyes, etc. other bad ingredients. 

How much is he vomiting?  Give his tummy a break from any kind of food for about 12 hours and give him some plain yogurt (not flavored) just about a tablespoon every hour or so.  Make sure he is drinking water and not dehydrated....he shouldn't be if it is just food intolerance.

Here is a web site to check out hot to determine good food from bad:  www.thedogfoodproject.com ....some high quality foods are Canidae, Innova/EVO, Merrick, Natural Balance and many others.

Yours are obviously not allergic to corn or grains and that's great. But feeding them that over the years can affect the health of some dogs as they age.  It's like us growing up and eating McDonalds our whole lives....it's not going to hurt you as soon as you eat it.  But it sure will hurt MOST people in the long run.  Do the research and you'll understand....this is certainly not just my opinion. 

What you choose to feed your dogs is your business but if a new member asks for help in choosing a food then I will tell the truth about foods.  Years ago I fed horrible food to my dogs (Purina, etc.) until my daughter and the members here on the forum showed me the research and how to research the quality of foods.  I want my dogs to live long, healthy lives.