Did you rig an airline tube to the valve on the top? I'd like to know how you did it, if you could explain.
It will be hard to build a bubble ladder, but you could try running it through an air stone unless you could get your folks to get a Hagen ladder that you sometimes see on Ebay or Aquabid for cheap. I think you might be able to order them from an online retailer for about $9 - can't recall where.
You could fix the CO2
tube into your filter intake also, or make a powerhead driven reactor with a water pump and a gravel vac rigid tube.
First off, you will need to measure your KH
and be sure you have enough buffering capacity to keep your pH stable.
I'll move this over to the Planted forum where CO2
is very frequently discussed.