I did the tests for the newly mixed water with RO/DI(0 TDS) too. The readings were 15 .
I have two tanks. My Salifert test ran out two weeks ago so I bought a new kit.
Everything was normal with the old Salifert Alkanility tests. My corals and fish are thriving. Ca and Mag are 400 and 1250.
I don't have any other brand except Hanna.
I figure it is most likely to be a bad batch.
