Whoops!, I am sorry, I totally forgot this thread!. Thanks for the comments guys
Xema, the chladophora is tied with nylon thread to a flat piece of slate. This algae grows very slow, but it does grow since I can no longer see the nylon.
Right now I am turning the cube into an ultralow-tech tank. besides it not having neither filtration nor heating I have now unplugged the CO2, and replaced the 11w CFL with a 60w incandescent bulb (which nicely heats the tank). You can say it is just a jar with water and plants, not an aquarium, but I am sure I can make it look good. Things are not easy though, I am getting some algae and stunning until I get used to the low nutrient uptake.
I have added Microsorum pteropus "narrow" to the lot, its amazing how fine the leaves of this plants can be, for a Microsorum. I´ve also abandoned that manicured looks. I´ll post pictures soon.