I'm building a cold, water-based ocean-planet for my current setting, its temperature being below 0°c at all times and in all of its regions. Even despite the freezing temperatures, the planet's oceans are in a liquid state because of its thick, earth-like atmosphere, the large amounts of salt, ethanol and the biological anti-freeze proteins it contains due to local microbes. It's about 1.5 times as massive as earth and orbits its host-star just behind the system's frost-line.
My question would be: is this type of planet even stable to begin with? or would there be some chemical reactions taking place that would render it completely uninhabitable?