Here's what I've used to scape my biocube29 and other small tanks.
1.Take that rock out one at a time and keep a bucket of water handy.
2. As you take rock out one by one break them into smaller chunks ie, 4-6 pieces fir your largest 2-5 for the medium so in so forth.
3. Put pieces in the water bucket to rinse away debris and dust.
4.re scape with your now "scaled" down rock.
You lose no weight worth mentioning and gain the ability to scape it the same way you would say, a 125g. Just on a smaller scale. It looks super cool and proportioned correctly. I've also used those bags of rock rubble as well. But since your live and cycled I'd just break it up. That branch could make some cool "pedestals".