Sorry about the short reply...I was a bit rushed. UV
is rated, for our uses, by it's ZAP dose. This is the amount of UV
energy in mw/cm2 that the water is subjected to as it passes through the unit. Different organisms have different required doses. If I remember correctly, algae requires a ZAP dose of about 20,000. Some viruses require 400,000+ to kill them. A 9 watt sterilizer is pretty small and you'll need a very slow flow rate to be really effective. Check out the article I wrote in the articles section for more info on this...it explains it pretty well. I'd figure your flow rates at 50% of the recommended rate for the 15w unit. Don't believe the published rates by the manufacturer...they want to sell units.