PRODUCT FEATURES The black streaks in gutters are in the oxidation layer of the paint. F-13 removes the oxidation and in turn removing the streaks and unlike butyl-based products that when diluted with water lose their strength rapidly, F-13 is effective at dilution ratios of 50-1. F-13 can be used safely at dilution ratios as low as 5-1. 20-1 dilution normally removes the oxidation with light agitation, making F-13 very economical to use. F-13 works best in temperatures above 60 degrees. Reviews Featured Products F-13 Gutter Grenade Starting at $16.22 Choose Options (4 Pack of 1 Gallons) Cling-On $93.67 $112.20 Add to Cart (4 Pack of 1 Gallons) Elemonator $98.53 $117.92 Add to Cart (4 Pack) F-8 Neutralizer / Brightener $32.13 $37.80 Add to Cart