What's your level of CO2 (ppm)? If I were you, with low light, drop the
level of CO2. FWIW, CO2 and O2 can exist independently of each other in
water, but sounds as if the level you have is too high for the light you
have. In my tank, with CO2, you can actually see the leave bubble O2, which
means the O2 level is supersaturated, and the fish don't have any problems.
Also be aware that there may also be a layer of CO2 on the surface of the
water due to CO2 being heavier than air, which may reduce O2 exchange.

Cheeers,
Poe

"François Arsenault" wrote in message
...

One thing that should help in the near futre is an increase in the amount
of
light my plants get. I've always known I don't have enough light, but I
only
recently realized just how bad the situation is. At the moment, I only
have
about 0.6 watts/gallon (a single 25 watt tube for a 40 gallon tank). I
understand 2 or even 3 wpg would be closer to what I need, so it seems I
desperately need to add a few lamps, which I intend to in the next few
weeks. I'm hoping my plants will do a lot better, using more of the
injected
CO2 and producing more oxygen. If it happens, the neons should fare much
better. I hope they stop hanging in the back corner then.