Co2 and O2
 

I have a R75g, And inject Co2 wtih compressed gas. My absorbed level
is usaually always 15-18 ppm. I add ferts on a regular schedule. My
question is sometime the bubbles(o2 pearling) dont seem to be as good
as some days even after water changes? Is this normal? The tank was
setup again with all new substrate 2 months ago. So I do have brown
algea but it seems to be under control. Ive read that it is normal to
have this with (newly setup tanks. I thougth maybe that this could
have something to do with this.