Some pre-service mathematics teachers in South Africa are nervous about the content of Euclidean geometry because they did not study Euclidean geometry in high school but will be expected to teach same when they start their teaching career. Because of this, graduating pre-service mathematics teachers were enrolled for a six-week intervention programme that metamorphosed to this research. This research reported a mixed study design that explored how pre-service mathematics teachers' respond to tasks on similar triangles with respect to treatment and conversion transformation of semiotic representations. Sixty-five pre-service mathematics teachers response to a written task was analysed using descriptive statistics while the extract from semi-structured interview were analysed thematically. The main finding of this research revealed participants' determined attempt to improve their geometry content knowledge for teaching through visual representation. The research also revealed that many participants were able to answer those items requiring treatment of registers but struggled with those requiring conversion of the register. The interview confirmed some of these struggles experienced by the participants in solving the given task. This research recommended careful design of programmes for upgrading pre-service mathematics teachers' content knowledge for teaching school topics.