I'm stumped. Just tested my water today for nitrates using Salifert test kit. Been expecting it to be rather high as I've been feeding heavily daily (3 pumps of bioplankton, 3 pumps of coralplankton, some golden pearls per day) and I only have a small area (between 1-2 lunchbox size) of dsb in my sump. And I don't use liverock. Skimming using AquaC urchin (10 hrs a day). Have about 10 fish in about 50 gallons of water. Only changed 1 coralife bucket of water since my tank got running few months ago. Results came out undetectable nitrates. Could my test kit have expired? I only used it for like 4-5 times.