Oh, I think a large tank (75gal + ) could use 10ppm of NO3 in a 24 hour period. RedSea isn't a good nitrate test kit. I use Aquarium Pharm. brand, but even it isn't super accurate. Steve Hampton has done some test kit comparisons. If you want 100% reliability, you have to go with Hach or LaMotte. the next step down would be a SeaChem nitrogen test kit. Below that, something like AP.