DrWhipIt said:
Gutter Shock is amazinger.
The problems I ran into with Zap was that I had to brush too much and too often, it has a pretty nasty effect on bare aluminum window screens, and it'd take the paint off ocassionally.
With Gutter Shock I don't have any of those problems. I rarely have to brush at all, and when I do, it is in one or two stubborn spots, and it doesn't take much agitation at all. I spray it on (at about a 1:4 ratio of shock and water) with a pump up, and then rinse it off after a couple minutes dwell with a low pressure tip.
I've got a 5 gallon pail of zap if anyone wants it...You pick it up, you can have it.