I'd wait for the nitrites to show up before doing a 50% water change. There is no fish in the tank, plants like some ammonia - for them it is just nitrogen, its not toxic. Wait a few more days and test again. If your nitrates are still going up, fine. Do your water change. However, if your nitrates are the same and you still haven't seen nitrites I'd wait a couple more days after that to do your change - just to be safe.
Hopefully by the end of the week, your tank will be ready to go!
Cathy
Hopefully by the end of the week, your tank will be ready to go!
Cathy