In a status update, NASA said the leak was isolated to a hole that's about 2 millimeters (0.07 inches) in diameter in the orbital compartment of Russia's Soyuz MS-09 spacecraft, which is attached to the Russian-built Rassvet module on the station.
"Program officials and flight controllers are continuing to monitor the situation as the crew works through its troubleshooting procedures", said the latest NASA report on August 30.
The leak rate was minuscule, and the crew put Kapton tape over the hole to slow the loss of pressure even further.
"As the teams were discussing options, flight controllers in Moscow performed a partial increase of the station's atmosphere using the ISS Progress 70 cargo ship's oxygen supply".
Gerst, along with USA astronaut Serena Auñón-Chancellor and Russian cosmonaut Sergei Prokopyev, are due to use the same Soyuz vehicle to return to Earth at the end of the year. He reported that a small bubble had appeared in the seal and said, "I'm not sure how it should be removed".
Russia's space agency will carry out additional analysis for other leaks. However, ground controllers asked the crew to hold off on finishing the fix work until tomorrow and to keep an eye on it until then. Then, they used a piece of medical tape with epoxy resin to form a more durable patch.
Nasa has stressed that at no point were the astronauts in any danger. "Flight controllers in Houston are continuing to monitor station's cabin pressure in the wake of the fix".
The leak was detected Wednesday night - possibly from a micrometeorite strike - when it caused a small drop in cabin pressure.
Mission Control outside Moscow told the astronauts to let the sealant dry overnight and that more leak checks would be conducted Friday. However, the exact cause has yet to be determined.