The optimal value for pullup resistors depends on the I2C bus capacitance, the bus rise time, as well as what the device considers to be the voltage threshold of the logic signal.
There are many online resources which show how to calculate these values, but as a rule of thumb, try a resistor in the range of 3kΩ to 6kΩ for fast mode or a resistor in the range of 5kΩ to 12kΩ in standard mode.