You posted as I did.

That makes sense, re accelerated photosynthesis increases o2.

I have run co2 levels of 30ppm (all I have ever aimed for as I believed that to be the holy grail lmao seems I am about to be proven wrong again?) and never agitated the surface of the water and had no problems with fish behaviour at all, of course their respiration may have increased but there was no behavioural change that I could notice to signify this?

Of course with co2 concentrations beyond 30ppm this will obviously be a different story