Prime does not remove nitrates; it detoxifies them for around 24 hours. To get nitrate down you need to do water changes. The maximum recommended level is 20 ppm.
Once you have the test kit, test your tap water for nitrate. Some places have high nitrate in their tap water - UK legislation allows up to 50 ppm.
Edit to add - when you get the test kit, you'll read that the nitrate instructions say to shake one of the bottles before adding it to the test tube, then shake the test tube before starting to time it. These shakings are very important. One of the reagents settles on the bottom of the bottle and the shaking is to get it all back in to the liquid. The shaking before adding it to the tube - do it longer than it says. But once the drops have been added to the tube shake as the instructions say.
Once you have the test kit, test your tap water for nitrate. Some places have high nitrate in their tap water - UK legislation allows up to 50 ppm.
Edit to add - when you get the test kit, you'll read that the nitrate instructions say to shake one of the bottles before adding it to the test tube, then shake the test tube before starting to time it. These shakings are very important. One of the reagents settles on the bottom of the bottle and the shaking is to get it all back in to the liquid. The shaking before adding it to the tube - do it longer than it says. But once the drops have been added to the tube shake as the instructions say.
