Gjertsen is formerly the head coach of SwimAtlanta and is currently the head coach for Alamo Area Aquatics Association in San Antonio, Texas. He has served as the personal coach for one of the best Latvian swimmers, Andrejs Dūda. He currently serves as the personal coach for former American record holder Amanda Weir.
Gjertsen has been instrumental in the orchestration of the Atlanta Swim Across America event which he helped kickstart in 2015. Since 2015, the Atlanta event has raised over $3 million for cancer research, treatment, and development.