I have been able to test this using two other brands of test strips and a liquid test kit and found the water readings to vary dramatically at times. I'm not sure if the metal readings are accurate as I haven't had a chance to compare them yet but I would definitely NOT recommend these strips for testing nitrates and especially general hardness.
Jasonwell Magnetic Aquarium Fish Tank Glass Algae Cleaner - Floating Brush (L Size)
37 Review
π U-BCOO Aquarium Gravel Cleaner Fish Tank: Manual Siphon for Efficient Filter Gravel Cleaning and Water Change in Tanks
22 Review
Efficient 2-In-1 Magnetic Fish Tank Cleaner With Non-Slip Design And Scratch-Free Blades
37 Review
Steam cleaner Deerma Deerma DEM-ZQ610 EU, white/red
68 Review