Well Tom, for the firt time ever, in all the forums where I've seen your posts, I have to say I disagree. Please don't get mad at me.
When I firt setup my CO2 cylinder I used the selenoid valve to shut off CO2 during the night, I used a drop checker to make sure I had enough CO2 also. Well, I was more worried about having too much CO2 than not enough to tell you the truth so I checked on the drop checker before lights out. After a day of tweeking green, a little on the yellow side! Yay!
One morning, I decided to check the drop checker in the morning. Dark blue.
The dude at my LFS told me to shut it off at night to avoid PH swings. After all, plants do not consume any CO2 during the night. Well, it seems that by turning it off, I was getting huge PH swings, so I decided to keep it on at all times. I reduced my bpm count by almost half and low and behold! Green before lights on and green before lights off! Yay! My PH probe also confirmed that the PH was stable.
I have really soft water and my filter is way overpowered for my tank, so that probably is a factor for the PH swings at night woth no CO2. Even though the plants did not consume any CO2, the water just degased overnight.
Bonus: After keeping the CO2 on 24/7 for a month, pretty much all the BBA in my tank was gone! Hurray!
So was it due to the improper use of CO2 when the lights where on, eg your fault for not adding enough to begin with and keep it there, or is honestly due to adding 24/7 or anything remotely to do with pH?
I have far more wiggle room and buffer when I add CO2 only 10 hours of the day, vs chronic high levels 24/7. When the high CO2 is added, I alos have higher O2 levels to compensate. This aids and helps fish stress, respiration etc.
Algae is relatively easy to deal with and kills nothing really, CO2 can and does kill more fish than any other thing in planted tanks where it's used.
Neither my tanks nor Amano's ever uses CO2 at night. They do not have BBA either
So it's due to not adding CO2 24/7, the observatioins that we all know cannot explain your claim and also support what myself, Amano and others also see.
You are certainly welcomed to disagree, but why don't I or Amano also have BBA?
Skill? Maybe a tad, but more likely good usage of CO2.
I do not add for respiration and over dosing issues should it keep running 24/7 and when I sleep and do not keep an eye on the tank.
I also use 60% less less gas refills than 24/7 users.
Folks that add not enough to begin with during the day often have plenty of CO2 at the start of the day if they leave it on 24/7. If they do not do that, then the first few hours are lean/poor CO2 when the lights come on, so they get soem algae and other issues.
If they added more CO2, had better current, responsive CO2 diffusion etc, then adding CO2 only during the day is not an issue.
Still, this is not an issue of pH, never was. Nor an issue of "stability" whatever that means, it's simply about adding enough CO2 during the day time.
If you have to add it 24/7 to have it start off at a decent ppm and cannot figure out any other way to do it, then that's all you have to work with.
But.............that does not mean others are wrong, nor explains why myself and many others have little issue adding it during the day only.
I'd rather have the fish less stressed in terms of respiration.