c02 optimat works for a while - and then stops...
I bought a kit just to see what could be achieved for the small price - but i wouldnt recommend it as along term carbon dioxide source.
The plastic thing that the carbon dioxide resides in in the tank, has a membrane on the top of it that allows the carbon dioxide to slowly diffuse into the tankwater. - I find that the membrane gets clogged with algae very quickly and then needs to be scrubbed - which is probably damaging it over time.
My partner (i think) is buying me a propper set for crimbo.. (fingers crossed)
Its probably better for low light level tanks where the algae is less of a problem.
x