I'm assuming you're using a liquid test kit...
I would personally recheck the nitrate. If you don't pretty much murder the second test bottle of nitrate before adding the 10 drops, you can get false-positive readings.
If the reading is still that high, I would do water changes to bring the nitrate back down, and see if you get another spike. Nitrate levels over 30-40 ppm can stress your fishies.
Edit: Your nitrates will only drop if your plants are using them. How big is your tank? How many/what types of plants do you have? I only have a few plants in my 10 gallon, and it takes over a week for nitrates to even register.
Last edited by RainbowSocks; 07-28-2012 at 03:16 AM.