Excitations in spin ice fractionalize into de-confined magnetic monopoles that interact with each other via the magnetic Coulomb interaction. Substituting rare earth ions with nonmagnetic yttrium is predicted to introduce static monopole pairs in the dilute limit, and leads to a dipolar spin glass transition at high concentration. We are able to model the heat capacity and spin correlations for low concentrations, but for high concentrations the theory is unable to account for the heat capacity data. We propose to study large single crystals of composition Dy2-xYxTi2O7, where x = 0.3 and 1.5, using SXD, in order to understand the anomalous behaviour. We shall measure the average structures using neutron diffraction and the defect structures and any correlations between defects using diffuse neutron scattering. We shall then cool to base temperature to study the magnetic correlations.