It is still possible to clean some of the growth away with just a finger but not all of it and it is so sharp that even attempting to clear this caused scratching on my finger. I consider this to be a fail. If the stuff cannot keep this growth off for just 3 months then it cant keep it off for the 5 years minimum needed for it to be worthwhile or even cost effective, what is more once applied the PureSeal itself is not easily removed. I guess it is back to regular antifoul techniques.