Practicing chemists use models, diagrams, symbols, and figures to represent phenomena which cannot be detected by the human senses. Although research suggests that these external representations (ERs) can also be used to address the challenges that students have in learning chemistry, it is not clear how instructors' use of ERs aligns with their perceptions of student learning difficulties. In other words, do instructors use ERs to address what they perceive as students' major challenges in learning chemistry, or are they using ERs for other reasons? The answer to this question could have implications for the professional development of chemistry instructors, including both classroom instructors and laboratory facilitators. As a pilot study to guide the development of a larger project focused on the use and interpretation of ERs, we interviewed eleven general chemistry teaching assistants at a major university in the U.S. Southwest about their use of ERs when facilitating acid-base titration laboratory activities. Our data suggest that there is a lack of alignment between teaching assistants' primary reported use of ERs and the primary challenge that they perceive their students have when learning about acid-base titrations. We discuss potential reasons for this misalignment, as well as implications for teaching assistant training related to the use of ERs in the laboratory learning environment.