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Gd5Si2Ge2 is known for its giant magnetocaloric effect (GMCE), but also for its associated large hysteretic losses. These losses result in a significant reduction in the net cooling capacity of this material when it is used for magnetic cooling. Attempts have been made to reduce these losses by adding other elements, like iron. Individual Ge and Si substitutions have been reported, but in this paper we focus on the system where both elements were substituted simultaneously with different amounts of Fe, with an additional interest in the new Gd5(Si, Ge)3 phase that appears after the substitution. We found that when substituting iron in small quantities the MCE and the hysteresis losses remain high, with a small decrease in the Curie temperature, and the low-temperature XRD revealed that the structural transformation is still present. However, with an increasing amount of Fe the MCE was drastically reduced because of the newly formed Gd5(Si, Ge)3 phase. The magnetic transition temperature of this newly formed phase was investigated in all three substituted systems: Si, Ge and Si and Ge. This transition temperature was strongly affected by the type and the amount of substitution; however, the changes could not be directly related to the composition of the phases.