Ideally you want 0 ammonia, 0 nitrites, and 0-20 nitrAtes. Nitrates aren't as harmful as the others but you will want to watch them also. If your ammonia or nitrites hits .5 ppm
I'd do a PWC
to get it back down. The only way to remove nitrAtes is to do a PWC
or add some live plants that will consume the nitrates. Anything above, I think it was, 40ppm is potentially harmful to your fish. Prolonged exposure to high levels of nitrates can drastically shorten the lifespan of your fishy friends.
What you'll want to do is pour a glass of water from your tap, let it sit for a minute and then test it. You'll be suprised at what you find. My nitrates right from the tap is 10ppm. My tank never goes above 10ppm. I have a few live plants that help keep things balanced.