Have you tested your alk with another test kit to compare to the Trident? What is the expiration date on the reagents? I've only had weird calcium readings with the Trident towards the end of the reagent. It usually drifts up and not down for me. You could try to flush the back feed line out...
I got my AquaBiomic test back a while ago. When I upgraded, I used half a bag of Ocean Direct sand and the live rock from my 20-gallon system. I dose Zeobak once a week. The test showed a mature reef.