When you say NPT...is this a soil based tank or is this a planted tank with gravel substrate.....
What kind of test product are you using, have you tested your source water for ammonia, nitrite, nitrate and pH, if not, I would recommend that you run test on the source water.
Also, the plant food/ferts can cause false readings especially with new setup and plants that are not actively growing or if you have the wrong color temp light for the plants to use it.
How many days has the tank been setup, what is the stocking-number and species of livestock and what type of filter.
Tell us about your lights-age of bulbs, watts, kelvin and photoperiod...
Right now I would start making 50% water changes every day to every other day and stop adding ferts for now.
Last edited by Oldfishlady; 08-09-2012 at 11:19 AM.