Does algae consume oxygen? cus i have a nice brown algae back ground... also my filter outlets are under water and they do move the water on the surface a bit... just how much water agitation is needed? i really enjoy the nice quietness from the two fx5 outlets being under water and not having an air pump... i only have 2 o's and a small silver arrowana... i don't notice the fish lacking oxigen...well what do you guys think? i want to be sure

If you have a little surface aggitation that should be enough to help the Oxigen and CO2 diffuse from the water.
Just a lil ripple in the water should be enough.
Airstones are a nice addition if you like the look of them or in case you got very warm tankwater, as Oxigen will have a harder time dissolving in warmer water.
Above 30oC that is.
And imo algae are like plants that run a photosynthesis cycle as well, so they consume and produce both O2 and CO2, depending on the lightcycle provided.

most algae are dependent on nitrogen...thus, it doesn't affect oxygen
contents at the tank. nitrogen and food waste or waste of fishes are foods
for all kinds of algae.

all u need to know!

en.wikipedia.org/wiki/Algae