I pre-wash too. I bought some lovely fabric from E. Burns tent sale in Paducah about 3 years ago. My color catchers came out deep purple for about 5 washes. I was about ready to give up, but loved the fabric. Finally after many more washes, the water ran clear. I find that if I buy fabric from cheaper sources, there is no bleeding. But the better quality fabric bleed horribly. I do tend to buy fabric with deep color, not pastels. I have never heard of Synthropol, but will check it out.