Is there any problem mixing two different foods? I am wanting to mix ProPlan Chicken and Rice with ProPlan Performance. My dog is getting a little too skinny but I think the 30/20 Performance is a little too much. He is an inside dog and he gets worked a good bit but not as much as a dog on a pro's truck. I am just trying to get the balance right. I have tried increasing the amount and it is not really working. I just want to make sure by mixing the foods I am not going to be short changing him some how anything he would need. David