Was definitely the fact that they had to cgi the hair. It's such a random thing but had to be done else the effect of being underwater would seem too fake.
In movies, detail is super important, especially when it comes to cgi, so while it's easy to only focus on the heavy imagery:
It's nice to also see the more lightend work as well./
Did you guys notice that the hair was fake in Aquaman? Or were you too distracted by this?