In my story, people are trying to colonize an Ocean planet that orbit Ultra-cool red dwarf. (Based on this Wikipedia article a planet can retain Water in this type of stars with a mass around 0.08-0.11⊙ and avoid problems to a certain extent).
The planet has a mass of 4 and a radius of 1.7 (Where 1 = Earth) with an average temperature of 11°C, and an atmospheric pressure of 1 atm.
Can this water-planet have a safe atmosphere that won't damage the body and let you walk on it (Floating base, boats, etc) with only an oxygen mask naturally while maintaining an H2O Ocean?
I heard that CO2 will be sucked into the Ocean and change through a carbon cycle, making the atmosphere dominated by other gases such as nitrogen, is that true?