Arnoldi was born as the first son of nine children to Ernst Friedrich Arnoldi (1747–1828), merchant and councilor in Gotha, and Sabine Elisabeth, daughter of master needlemaker Johann Elias Krehl in Gotha, Hauptmarkt 38. His first marriage was in Weimar on September 21, 1808 to Rosine Wilhelmine Cronrath (1790–1823), daughter of the court carpenter Johann Wilhelm Cronrath. Wilhelmine must have been an extremely beautiful woman, because the privy councilor Johann Wolfgang Goethe requested a cast of a marble bust that Father Cronrath had had made by the Weimar sculptor Carl Gottlieb Weisser (1779–1815). With his first wife, Arnoldi had three sons and one daughter.
After the death of Wilhelmine, Arnoldi married Christiane Rosenberg in Gotha on January 30, 1825, this marriage remained childless. Arnoldi died on May 27, 1841 in his house at Hauptmarkt 14 and was buried in Cemetery II, opposite today's Arnoldischule Gymnasium.(...from Wiki)