From my observations thus far...and i apologize for the resurrection of the thread..but Fibrous taint along with tainted sheep/creepers and liquid taint (goo) are the only non node things that increase the spread of tainted biome. The EASIEST way to stop the taint growth is to simply walk the biome and destroy all of the crusted taint and fibrous taint as this will GREATLY stop the spread. Ethereal blooms are the fastest way to remove the taint biome altogether, even though they are expensive themselves. 20 of them do a fantastic job at removing the biome quickly if your attentive to moving them.