I'm not a CO2 user <"Are co2 enriched tanks really fair on the critters?">. I never will be, but if I was? I'd dial the CO2 addition <"down to ~15 ppm">.
I'll need to find a reference, but I'm pretty sure that they are largely independent. As I said I don't have any practical experience of adding CO2, but this was what @plantbrain (Tom Barr) said in 2011 <"Oxygen in a planted tank."> and Clive (@ceg4048 ) in 2014 <"CO2 stability, brush algae and EI water change">. I think they have probably pushed the CO2 level higher than most other people
It's like a glass jar that uses hydrogen peroxide and a catalyst to produce micro bubbles of pure oxygen that dissolve straight into the water. There are some additional marketing claims about 'active oxygen' also being produced but I think these are nonsense on a par with products like seachem matrix. They do help oxygenate water though without creating a lot of flow or surface agitation.
I have just started my entry into CO2 injection and have made an active decision to aim for 15-20PPM and plants that suit.
I didn’t notice much growth difference with more co2 than “some” co2 either. I think 15-20 works quite well if you have a relaxed-gardener approach.
I wonder if you had an oxydator or oxydators working well enough whether you could achieve pearling from plants without co2 by achieving oxygen saturation without an airstone or something creating a lot of visible bubbles.
I did this. The oxydator is a neat, simple little device, and it definitely put out a steady stream of O2, but I didn't notice any great effect on my plants or livestock and ended up getting tired of replacing the H202 and scrapped it. Without a DO meter, I was unable to confirm an increase in oxygen in the tank, but I assume it helped somewhat. My understanding regarding CO2 and O is the same as dw1305's -- dissolved oxygen does not displace dissolved CO2 in the water column, rather they are independent. It may seem that CO2 reduces oxygen due to two phenomena, i.e. that excessive CO2 makes it difficult for fish to breathe and an airstone will reduce the amount of CO2 in a tank, but neither is due to the dissolved oxygen displacing dissolved CO2 in the water column, but rather they are due to how fish breathe and the increase in gaseous exchange at the surface caused by the airstone.
Pearling is possible without CO2 or any extra equipment if conditions are right! I typically see it every day in my higher light tank. Some plants are more prone to it than others, and while I always consider it a good sign, you can have a perfectly happy tank that never does it.
You are right, a lot depends on the conditions, and even <"very eutrophic water"> can feature pearling in the <"right circumstances">.
Ok, if your algae is pearling that is not a positive sign for your tank! 🤣
