(Acgelok) wrote in message ...
Hi y'all, can any-one on this forum tell me witch is heavier D.I.Y. CO2 or
atmospheric air (air we breathe)? It has to do with an air-space at the top of
my D.I.Y. CO2 setup. I dont know if I should vent it or ignore it

Tightly enclosed tanks can accumulate CO2 in the air space, and will
need an air pump with airstone to correct this. These tanks had this
problem:

http://www.svas.info/Newsletter/sam.html

When it was first set up, the tank on the left had fish gasping at the
surface less than half a day after CO2 was turned on.

On the other hand, most tanks with even a little air circulation under
the hood do not need any help. The CO2 diffuses into the atmosphere
pretty quickly.