algae question

[rogergolf66]

is there a macro algae or bad algae that absorbs O2 and puts out CO2?

I ask because I'm having an odd algae again that came and went last year and had the same low ph issues last year when this algae was in the tank both times now.

 

[Secondsbest]

At night, when algae and plants are not using sunlight for photosynthesis, they can respirate O2 into CO2. This happens in aquaria with the lights off. In marine tanks running adequate skimmers, and having moderate algae amounts, PH swings are not a concern. If you don't meet those criteria, running an algae grow out tank light opposite the display will temper swings.