Fishless Cycling Question

[smokedetecor]

I am on 21 days of fishless cycling a 20 gallon tank with no live plants. I used sponge media to cycle the tank. The tank has been converting 4ppm ammonia in 24 hours for about a week. My nitrites have been off the charts for a week also. This morning I tested and the Nitrites are 0 ppm and 0ppm Ammonia. The question I have is my tank cycled? I am confused because my Nitrates never spiked. They have been consistent around 5 to 20 ppm for a week. I was going to add fish tomorrow do I need a water change or am I okay because my nitrates are low?

 

[jetajockey]

I'd give it a few more days, keep dosing and make sure that the nitrite => nitrate bacteria colony is well established.