The color density (saturation) is not going to match the card when held next to it. Try holding it and viewing it at different angles to minimize this difference (that's what I do). The tone, shade, value is what you want to match to get a reading. But for nitrate it's not that important--the difference between 5ppm and 10ppm is of no practical consequence. The difference from week to week can tell you something about how much ammonia is being processed.
You can wiggle the dropper part out of the bottle, carefully, with pliers. Put a BB-sized bead or bit of gravel in there and close it up.
Okay, so for the liquid test....Is the actual color of the liquid the result, or the color I see when I hold the test tube right up against the card (touching). Because there is a dramatic difference...The color of the liquid says five....Up against the paper it says ten. Ugh.
ETA: Ah! I know why you have lower nitrates than I do...You have no chloramines and therefore no ammonia in your source water!
Ah well...10-20ppm nitrate by the end of the week is fine with me and probably fine with my fish, however, 5 would bring much more piece of mind /:
Thanks for admiring my fish, fff. Not many members liked him in the photo contests.
Actually, he's a "Copper," three translucent layers of color. Depending on the light intensity and angle, he can look copper-tarnish green, dull blue or (mostly) copper-penny brown. But he's so shiny I can't get a good picture of this color mode. He's a 4-ray HMPK and proud of it.
The light blue HM in my album was my dragon-scale---a devil-dragon because of his red fins. Some people consider dragons as only white. Some include light blue as dragons.