Moorish Idol - Take 2

[Aquattro]

Originally Posted by Samw

Are lights off? if you have your lights on and have algae, you would be getting pure O2 from photosynthethis from the algaes in your tank.

Alternatively, lots of algae will contribute CO2 at night, which is when I lost my fish.

[Samw]

Originally Posted by Aquattro

Alternatively, lots of algae will contribute CO2 at night, which is when I lost my fish.

Yes, that's why for this test, one could turn off the lights to increase the depletion of O2 in the tank. See Eric's clownfish tank test where his DO dropped to 16% at night. And overflows are like waterfalls I guess so that is probably oxygenating the water. If that water is coming back into the display at large volumes, then the display tank is oxygenated no matter whether lights are on or off.