Total nitrate is calculated by taking the nitrogen-nitrate reading your test gave you, and multiplying that number by 4.4. Normally the instructions that come with the test will say so. Some do not. If you are unsure about what your test really measures, you can always resort to calling the manufacturer. This is extremely high, and sure to endanger your corals and your fish as well.
Fish suffer from high nitrate levels in the tank too.
There is another document on our web site that deals with this in more detail. High phosphate levels may contribute to this too, as they will result in wild, and sometimes totally unexpected, growths of undesirable micro-algae. The real danger lurks when encrusting diatoms start to grow on the skeleton of the coral, start moving upwards along the skeleton, reach the polyp, and start pushing the polyp out of the way. Besides the water quality deterioration or bad condition of it, there are other other causes that can lead to the onset of bacterial infections. The main ones are related to damage that occurred to a coral, as the damaged area gets infected and bacterial disease follows.