Question about my quarantine tank

[Tguzler]

I setup my 35g tank as a quarantine tank with a couple small pieces of live rock and live sand. I let it cycle for 2 weeks prior to adding fish. I am running a hang on the back Quite Flow filter, I recently added a couple of clowns and used Prosi-Pro to combat any problems. The issue I am having is that with the Prosi-Pro I need to remove my carbon filter and limit my water changes so not dilute the meds but in the meantime my Nitrite has raised to 1.0, at what point do I abandon the meds and put my filter back in and do a water change?

Tank number
PH 8.0
Amonia 0
Nitrite 1.0
Nitrate 15

Thanks