so what kind of macros should i put in there?
It's really personal preference. A lot of people grow chaeto because it's a quick grower and fairly easy. I grow a lot of different types of caulerpa, graciliara and other red algae because I have a display refugium, so it needs to be neater than one that's hidden under the tank.
Some algae, such as halimeda, sucks calcium from the water, so use those sparingly.