Pete wrote:

I still loose a little CO2, but that's probably because I drive them
quite hard at around 8 bubbles/sec. This gets my pH down from around
7.2ish to 6.2ish within an hour of the lights coming on.

1pH? That's quite a CO2 loss. My tanks stay at the same level during the
night after the CO2 cuts out. I think that's because my plants produce
just enough CO2 to counterbalance the loss that occurs through surface
agitation. I have very little agitation happening at the water surface
though. How do you count 8 bubbles per second? My brain just don't work
that fast!

Nikki