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Can anyone explain "Phytoncide"?

http://en.wikipedia.org/wiki/Phytoncide

 

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In my experience, I have seen algae blooms when something happens that interferes with my plants' steady growth.

Same here. My CO2 ran low a couple weeks back and bam! Plant growth came to a screeching halt and BGA was all over the glosso the next morning.

Bumping my CO2 back up and increasing NO3 didn't do anything to the algae, it merely got the plants humming along again, which _stopped_ the algae from growing any further. It didn't get rid of it until I cut the lighting and killed it off. Hasn't come back.

The happy plants have some magic something they secrete into the water column that makes algae very unhappy.

 

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I believe that O2 concentration is linked to algae outbreaks. I have a BBA outbreak whenever we have a heat wave. It goes away after a couple weeks without treatment. The local lake/pond also has a nasty, smelly algae outbreak soon after a heat wave. There's a known relationship between temp and O2 concentration. When water temp rises, O2 concentration drops.

Yes, but plants also don't grow as well in hotter temperatures.. most plants anyway. As the temps rise the growth slows and algae gets a foothold. I've never heard of any relationship between oxygen and algae.