If im not mistaken No3 at 10ppm is safe for fish. If your NH3 and No2 are 0 you're done with the cycle and can do a water change and begin adding fish. You're going to have issues with your trates for a while, untill you build enough bacteria in the sand bed and rocks to convert your trates to regular Hydrogen. You could do some carbon dosing like Vinegar, Vodka, Biopellets or even GFO, but i wouldnt worry too much about it yet. Reg water changes and vacuuming the SB would suffice.