The Karlsruhe Tritium Neutrino (KATRIN) experiment aims to determine the effective mass of the electron antineutrino by investigating the tritium β-spectrum close to the energetic endpoint. To achieve this, there are stringent and challenging requirements on the stability of the gaseous tritium source. The tritium loop system has the task to provide the <0.1 % stabilized flow rate of tritium gas into the KATRIN source with a throughput of 40 g/day and a tritium purity>95 %. KATRIN started full tritium operation in early 2019. This paper focusses on the observed radiochemical effects and confirms that non-negligible quantities during initial tritium operation have to be expected.