NO3 tested at 10 tonight on Salifert, down from 25, so the Nopox is doing it’s job. Didn’t test PO4 but I will soon. My skimmer is not producing much lately so I was a little concerned about the Nopox. It will be interesting to see where PO4 is. My back chambers are dirty again so it’s probably about time for another deep clean out back there. My sand needs a good cleaning as well. Not my favorite activities but they need to be done. It’s frustrating not to be able to keep the back chambers clean.