Another thing to bear in mind is that when a tester reads the highest colour on the chart the actual level could be that value or anything above that value. If the shop used a tester with 5 ppm as the highest colour, your nitrite level could be 5 or anything over 5.
The danger with your current tester is that you can be misled into thinking the cycle has finished when there's still nitrite in the water.
The danger with your current tester is that you can be misled into thinking the cycle has finished when there's still nitrite in the water.