Originally Posted by Race3370
What kind of gas exchange?? I guess I have never heard of this. Any more information would be greatly appreciated!!
Having an open top gives your tank a lot more surface area between your water and the open air. This gives you better gas exchange between the water and air when compared to a closed glass lid. This is ultimately healthier for your tank as oxygen can be reintroduced to your tank and CO2
is released from your water.
However, with an open top, there is a chance for your fish to jump out etc. A good way around this is with a canopy, or like I suggested above, a screen mesh top.