Originally Posted by Bunbuku
If you keep the HC trimmed very short (<1"). It will be less likely to lift off the substrate. Some folks also cutout patches of carpet to give it room to crawl sideways. I have the same iwagumi starting its second yr in my 60P. In that time I replanted the carpet about 3 times in the same Amazonia substrate. After I push the HC plugs in, I just sprinkle a layer of Amazonia powder type and stuck in a few sticks of Multibottom - then it's good to go! You could put more soil on top but you will still need to trim. Plus fresh Amazonia will give you a little NH3 spike which your livestock probably won't like.
Pretty much this.
But, as long as your HC is growing well and sending out deep roots it won't come up. I had my 20L ~80% carpeted with HC at one point and never had issues with it lifting up. All I had to do was keep it trimmed and it was happy. Every 2 weeks seemed to be the regular.