i had modifed the above to act as a mini surface skimmer and co2 reactor.
sorry, no d-cam....has to read the following...

drilled two holes at the top of the extra compartment.
pulled in a tube A into one and co2 tubing B into another hole.

pulled A all the way to the bottom of the compartment and but the tubing at an angle so that it lay flat onto the filter media. cut the other end to required height of your water level is. (i cut a 3cm angle) if water level drop below it....hmmm... no skimming action. i'm still working on this so that it float. note that this skimmer is slow as the size of inlet is only a tuber.

pulled B into the compartment. w/ or w/o diffuser (an UP atomizer diffusor is advisable, just nice for fitting.) w/o diffuser; this act as an invert bell, storing the CO2 at the compartment and the suction of the filer will dissolve the co2 through the filter media. w/ diffuser; the fine bubbles will be suck in through the filter media as well.

at least this save me a lot of space of getting a standalone diffuser in my 1ft cube tank.

try it at your own risk hor...