Just wanted to point out that op said life rock, not live rock. Life rock is the CaribSea brand of dry rock.You may be getting false readings as if it is truly live rock and you have added Bacteria. . . . You may very well be at zero but it needs to be verified. If youre using API test kit- It may be a false reading. If not. . Take A WATER Sample to a ested Store that does NOT use API kit and have them test for you to see what they come up with and to compare with your results.