Robin Pereira wrote:

I believe Nitrates are about 10 ppm. but I don't entirely believe the tests
because the value never seems to change. Phosphates are zero. I don't test
iron. Ammonia & Nitrite are zero.
I change 20% of the water weekly during tank maintenance.
I dose 40ml. Tropica Master Grow/Wk. and add 10ml. Potassium Nitrate (mixed
using info from Chuck Gadd's site).

If you doubt your test kit, and you have KNO3 in house, just do this:

1. Do a test and carefully observe the color
2. sprinkle a granule or two dry KNO3 into the test vial. Note the immediate
color change.

The more you add, the more it should change...