Refugium is indeed amazing.
I am currently using a basket chaeto as nutrient export. But as I don't stay in a landed property where space is not a concern, (even if I do, I doubt I'll dedicated a similar size chaeto tank as my main tank)... As small quantity of chaeto/mangrove alone is not enough to export the nutrients.
Again, this is based on my personal "trial". Never try, never know... Actually I could be wrong, but iwarna's outdoor pond does have skimmer too right? A 6' tall Beckett??
Another great use of having a refugium, pods growth! It's amazing how much (and big) pods you get...
Downside, without proper circulation, refugium collects detritus.. So dont forget to do the regular clean up maintenance.