pink,red antifreeze and problems

Well, I thought that I was doing something good for my van when I had a new radiator put in 20,000 miles ago. I had that 5yr 150,000 mile antifreeze put in the whole system. The pink stuff. Today I see my radiator leaking and take it to the shop that did the original work. They show me this nasty gray putty type crap that is in the radiator. He just stuck his finger in the filler tube and there it was. He told me a bunch of horror stories about that antifreeze and suggests going back to green. I had all my vehicles switched over to the pink. I guess I'll have to flush them all out and find something different.
Anyone have this problem and what did you do or suggest?
HELP :confused: