lately I have been having more luck with my icing when I do a few things. before I start the icing I clean the bowl, blades and all utensils with vinegar. Next, I stopped using a whisk, and now I use mixing blades. After I make color and prepare the frosting I let it set for at least 5 minutes before using. The bubbles rise to the top while it sits. I have fewer bubbles and craters with a PME 1.5 tip.
Good luck.