Review on Copper Test Kit: Accurate 90-Test Aquarium Water Testing with API by Karyn Garcia

I used this to control the copper concentration in the pool. My target concentration is 0.3 ppm or less. I tested my water samples at Leslie's pool supply store and they showed 0.3ppm copper in my water sample. But my API kit test didn't give me enough color changes. The color I got was closer to 0ppm than 0.25ppm. Actually I don't know which measurement between Leslies kit or API is more reliable. But what I can say is that a color change of about 0.25ppm is not sensitive enough for this test kit.