General hardness just means your water has a lot of dissolved minerals in there. It is not something you need to really worry about. These minerals are needed in your tank, they are important for the health of your fish, as well as for buffering the ph. If your tap water has very high Gh and Kh you may want to stock your tank with fish that like that kind of water. I think most cichlids would do well!
Your Nitrites however are something to worry about. If you don't have a liquid test kit to tell you a more accurate reading, then it would be advisable to get one. Having high Nitrite readings means that your tank is not yet cycled, or has lost its cycle. Any time you have more than 0 Ammonia, and/or 0 Nitrite you need to regularly check those and do a lot of water changes (with dechlorinated water) to keep those as close to 0 as you can.
Fish get stressed living in those kind of conditions and are more susceptible to diseases (like ich). These toxins can also permanently damage their organs, and prolongued exposure or very high readings of these toxins can cause death!
If it is NitrAtes you meant, these are normal in a tank, but you have to keep the reading of these low also, by doing weekly water changes. Most people aim for NitrAtes of 10-20, but there are people who can keep them even higher than that if they have heavily planted tanks. The plants will use these Nitrates as food!
