I experienced that my Nitrates were at 20ppm until I used Distilled Water from the supermarket. It worked almost instantly. Now that I remember I am almost sure that it dropped to zero overnight. My tap water was my problem as to why my Nitrates were so high.
55g Reef Setup: 2 Percula Clownfish,5 Blue Legged Hermit Crabs,1 small Kenya Tree Coral,1 Toadstool,2 Yellow Sponge, and 1 Firefish.