A series of static adsorption/precipitation tests has been carried out to examine the behaviour of Diethylenetriamine Penta Methylene Phosphonic (DETPMP), a commonly used commercial scale inhibitor (SI), when in contact with brine and calcium carbonate (CaCO3). These tests are carried out at pH 2 and pH 4 and at a range of DETPMP concentrations from 0ppm to 5000 ppm. In these tests, the addition of disaggregated CaCO3 to the brine/SI mixture was accompanied by a rise in the pH and a commensurate precipitation of a DETPMP_Ca complex. Apparent adsorption displayed a common 2:1 trend indicating that no adsorption took place, only precipitation. These results changed somewhat when selected divalents (Ca and Mg) were removed from the brine.