Shoot, it's been a while! I still haven't added the dirt, because to be honest I completely forgot about it. I had it soaking in a bucket in the basement, and it's definitely waterlogged by now. I'll be adding it tomorrow probably!
The tank experienced several happy days of growth, but now things are slowing down again. At this point I have no idea what to do, because I've already done multiple huge water changes and an ICP test, and the Cuprisorb doesn't seem to be doing much as it hasn't changed color. I'm not adding anything weird to the tank, and the nutrient levels aren't too high.
The monti caps are doing great, at least...