I have a 2 cu ft moderately planted tank with two T5 15w tubes, based on
what I have read here, I built myself a CO2 system out of two pop bottles
and airline tubing, has been running for a couple of days and now the CO2 is
bubbling at the rate of approximately one bubble per second. As it's running
directly out of the airline tube, a lot of this is wasted and just goes out
the top of the tank (I accidentally broke my airstone). I'm rather concerned
that this will adversely affect the fish, inasmuch as that there will be too
much CO2 in the water, too high a pH and that as CO2 is generally heavier
than air, what is not absorbed by the water will collect over the tank
between water level and tank rim and basically suffocate the fish! There are
certainly a lot more bubbles on the plants anyway.

Regarding the lighting, I originally got one T5 15w tube approximately 5
months ago, and another one last month. Will this be enough for the tank? At
what intervals should I replace the tubes?

Any comments would be appreciated...

Marcus