your system is kind of silly.
first you diffuse off a disk,
then you recombine the bubbles in a tube,
only to be disbursed by a small powerhead?
take the tube away, and lower the powerhead,
so the disk diffused bubbles rise up and get
blown around by the powerhead a bit
before they reach the surface and pop, or
get rid of the powerhead entirely as it's surface
agitation only releases more Co2 into the room air.
at least you have cool looking check valve