I usually get about 25-30ppm of CO2. After a while I didn't bother to check
since the plants were flourishing and everything was great. However, in the
last month I've been noticing algae that I've never had before, namely the
green spot algae on some of the leaves and some strings of staghorn. I
checked the CO2 last week and was surprised to see only 19ppm. I usually
change the bottle every week after a water change (on Sundays). So today I
check it again this week and it's even lower!!---12ppm! What the hell is
going on?

I have an airline that is feeding the bubbles directly into my intake on my
aquaclear filter with a diffuser on the end. The fine stream of bubbles seem
to be pouring out like crazy just like when I had a higher concentration of
CO2...so there's no leak or anything---I'm getting a huge amount of bubble
action.

I did buy a different brand of yeast last month...and that's the only thing
that has changed. But why would that make a difference if I'm getting the
same amount of bubble activity?

Thanx for any help you can suggest,

Dave.