There are so many things you did with your icing I’m not sure where to start. First, don’t use warm water. Second, don’t use a whisk or put it on high. Actually less mixing is better than more. I always use C&H sugar, I’ve never used organic powdered sugar. My current choice of meringue powder is genies magic meringue powder. I use the recipe on the container. Also, before i start I clean everything with vinegar. It helps to get rid of any oil which will ruin your icing. Also, I don’t sift my powdered sugar. The one time I did it never set. Hope it helps.