Is that right that your tap water has 30 NO3?!
If your tap water has nitrate that can't be good, and no wonder your tank before had high nitrates! I bet Buck will have you shipping him your water now, or hook up a pump to the tap... lol!
The high nitrates in your tap is a very large excuse to increase your CO2 and lighting so you get some fast growth! You should never have to worry about buying any KNO3 if 30 ppm is your constant reading from the tap!