Yes, your water will test fine at first. The problem is not the initial water quality, usually.

This is (briefly!) what happens in a new tank:

For any closed environment, like a fish tank, to operate properly waste must be broken down before it becomes toxic to the animals. Waste is created from food, fish waste, dead fish and plants decaying in the tank. In a healthy, mature tank, there is a large colony of healthful bacteria residing in the gravel and the filters. These bacteria consume the waste products before they can decay and become toxic. This is repeated constantly. It is call a biological filter, and when it works, it works very well for a very long time.

The problem with a new tank, however, is that it is too clean and sterile. There are no bacteria living in there, therefore there is nothing to consume the waste products. They decay and release amonia. Amonia (I don't think I'm spelling that right?) is toxic, and will weaken, stress or kill your fish. The next stop of the process is that amonia is converted to nitrates, and then nitrates are converted to nitrates. Eventually, the cycle catches up with itself, and enough bacteria are present to take over. The problem, though, is that often times the fish die during the process.

Their is a process called fishless cycling by which one forces the tank through this amonia/nitrite/nitrate cycle quickly, with chemicals. After it is complete, the tank is biologically ready for fish. If your fish do die, you might want to clean your tank and start again with fishless cycling. There are many good sites on the internet that will give you the details on how to do it properly.

However, let's assume that won't happen. First of all, get your PH to 7.0. Nitrate is broken down into two sub-compounds, NH3 and NH4, one is harmful, one is not so bad. You will have more harmful nitrates at any PH other than neutral 7.0. This is very simple to do, just buy a kit and follow the directions.

You can buy bacterially loaded products to add to the water, which will speed the growth of the bacteria base. I have used Bio Denitrator and Bio Zyme in the past. They don't always work, but it's worth a shot.

You are most likely to have chemical spikes at approximately 15, 30 and 45 days. Test for amonia and nitrite/nitrates with test kits. You can buy products that will neutralize these elements. Also, do not be negligent in your partial water changes.

And don't freak out or feel bad about this! I would venture to say everyone that has fish started out with a big "oops!" with their first tank or two. It's manageable and fixable!!