Magnetic after-effect phenomena in polycrystalline Gadolinium Iron Garnets (GdIG) doped with calcium are analyzed by means of magnetic disaccommodation techniques. The results are presented as isochronal spectra in which the relative variation of the initial magnetic permeability after specimen demagnetization is plotted at different time windows. These results reveal that the addition of Ca ions in the garnet lattice changes drastically the spectra, appearing three positive peaks at temperatures around 150, 240 and 350 K. The features of these processes are strongly influenced by the amount of Ca doping and the presence of the compensation temperature around 280 K, which, on the contrary, depends just slightly on doping. These phenomena seem to be related with the formation of Fe4+ ions in the crystal lattice by electronic hopping. Some reasonable speculations about the mechanisms responsible for these behaviours are pointed out.