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Yes. Since plants give off oxygen during photosynthesis, these bubbles are constantly being produced. It is only at a specific interval or time that the water is so saturated with oxygen that the small microscopic bubbles gather together to form a big one which is then visible to the naked eye.
It's results like these that make me wonder at the spectacular tank you'll have if you ever go high light with all the bells and whistles. Simply amazing.
Wow, now that's impressive! See, its tanks like this that give us hobbyists hope to keep chugging along when everything appears hopeless. I don't think you should move over to CO2, there's no need! Very nice job.