Flow rate for 13Watt is 600gph for pond up to 1200; koi pond up to 600gal. 18Watt is for 800gph - 1600pond; 800 koi pond. 13Watt and 18Watt have 1 inch to 1-1/2 inch barb fittings.
All Biostep UVs have a 1-year warranty (excludes bulb); 15' cord; 1 1/4"MPT outlet with barb adapter for 1/2" to 1 1/4" tubing. Included are 1/2" to 1 1/4" fittings x two.