Hi. That is a great idea to use the refugium as a macroalgae display tank :)

We have a section especially for macroalgae which are just perfect to place in the display tank which you can find HERE

Especially red macroalgae species like Gracilaria & Halymenia will fit well for your purpose and add a great colour too to enjoy.

If you have the space in your refugium I would recommend some caulerpa species which we have not added to this section, as they might overgrow in a main display tank easily rockwork and corals. But I guess you won't have this in the refugium, or?

The Caulerpa Taxifolia, Caulerpa Prolifera and Caulerpa Racemosa are great for this.
The Ochtodes and Red Turf Macroalgae I would place away from the return pump, as they will attach themselves and floating parts might not be the best idea for the return pump :)

If you have any further questions let me know.

I hope you will find some nice macroalgae to kickstart your new project.

All the best and please stay safe and well.

Manfred

Livealgae UK