I'm a little confused, but if you are saying that NH3 and NO2 are 0, then sounds like you're cycled. Get precise numbers for NO3, not just "high", "low", or "off the charts". These are meaningless.
NO3 has no short term toxicity, but it is an excellent indicator of the amount of dissolved organic carbon (DOC) in your water, which you cannot measure directly. DOC is generally something that you want to keep low, it's an umbrella name for pollutants such as fish hormones and breakdown products of uneaten food, fish wastes, plant matter, etc. Establish a weekly maintenance routine that keeps your NO3 level (prior to water change) below 20 ppm. Doing so will ensure the long term health of your fish, and while it may be a little extra work, it will also save you loads in medication. Keep the water clean and the fish will look after themselves, let DOCs build up, and the pollutant-induced stress will weaken their immune systems. At that stage your fish will be more susceptible to parasites and disease.