Would this refugium be too small?

[Rippin]

Hi all,

So I'm in the process of plumbing a new 120g and 30g sump.
I'm considering dividing the sump to have a refugium, but with the large skimmer and bubble trap walls it only leaves me a small amount of space - approximately 8.5"x11"x16" or 6.5 US gallons. I do not have space to fit a larger sump under the tank and I do not want a refugium outside of the aquarium stand.

I was only planning on having macro algae and live rock/rubble in the refugium. Some sources recommend 20% of your overall water volume, which would be in the range of 24-30 gallons.

Is it worth it with only 6.5 gallons to spare?