BRS recently released an interesting video on the effect of curing their pukani dry rock. Check it out. I'm not trying to convince you or anything. Personally, I wouldn't risk putting small frags in a non zero nitrate system as I've had less than pleasant related experience. While 30ppm may kill them within a week, 5ppm would do it nice and slow. And that is assuming the test kit was actually accurate, which is almost never the case. On the flip side, my full size colonies were all fat and happy.