Thank you very much Gerald, I was sure that I didn't get the weights correctly
Resin doesn't remove only NO3, I noticed that it also clears the water from tannins (and who knows what else). You are right that in a planted tank it doesn't make much sense to use it (at least 24/7). I will keep the resin at hand and use it only in case of emergency or when I want to clear up the water visually. But I am happy to know that even constant usage should not present health hazard to inhabitants or plants.