I'm a known CO2 nag.

95% of the post I make about algae are generally not enough CO2.
Oh don't worry, I have to take my own advice too
Darnnit

But even the best of aquarist gets nailed and lulled into thinking their CO2 is fine, when it's not. It happens to everyone at some point and you will swear it cannot be, but then it is.
A simple method to see this effect is to make a few assumptions:

1. Provide non limiting nutrtients in the inorganic form in the water column: large water change and dose thereafter and note growth of plants. Plants will respond rapidly within and day or to 1 week perhaps in severe cases if you have corrected the issue, same for CO2.

2. Light, simply have enough, this can be quite low actually.

3. Well, not much else is left now. Just CO2.
pH/KH charts can be inaccurate depending on the water, ADA aqua soil substrates, driftwood, tannins, non carbonate hydroxide alkalinity etc.
Routinely on the web, calibrated test kits, pH meters suggest 200ppm of CO2 and fish and plants are fine. This would suggest other issues occuring, the livestock would all be dead at such levels.
Some folks slowly and progressively add more CO2 each day and note plant/algae, fish health during this time. Be conservative here. Plants can be brought back pretty easily from algae, fish can not be reanimated

Current is important here.
Many make the mistake of not having enough, seeing their fish gasp and assuming it's from the CO2, it is to some degree, but it's really low O2, the CO2 just adds to the stress, when good current and surface moevement is added, the fish are fine at the same CO2 ppm level suddenly, colors return, behavior is enhanced etc.

Make sure the filters are cleaned and don't reduce flow that much.
Cleaning is a basic thing, but many forget about the gravel also, it's should be vacuumed or fluffed up once a year or more in some cases.

This is a drain on O2 levels so it's removal of the detritus is a wise idea when everything else seems fine. It will not hurt either.

I generally will blast the current in the path of the CO2 diffuser and have it make a nice flow pattern around the tank for the best results.

Hi Tom, just noticed this thread.
Can you elaborate more on the connection between low O2 and algae? Is there any affinity for algae to low O2 in which algae is awaken when low O2 occurs?
Thanks.

I'm really only going to comment on the "blast the current" statement, but I had to leave in the "even the best of aquarist" part, just to establish where I fit in!

I currently have my powerhead-for-circulation and filtration at the opposite end of the tank from the internal venturi reactor. I keep thinking I am not getting the circulation I should be at the end opposite the circulation powerhead, even though it does create a strong currrent across the front glass. So, would it be a better idea to move that powerhead to the same end of the tank as the reactor, so it can have a better shot at moving the CO2 mist around? Right now the reactor does not create much of any circulaton by itself.

I get major pearling of almost all of my plants within a couple or three hours, which I was assuming meant that my CO2 level is acceptable, but I still get some BBA, which I assume means the opposite. So, maybe working on circulation is the next job.

It's a correlation, namely due to low plant growth I would say and rotting plant leaves. But we'd have to look at it and test to see if low O2 would indeed do this, thus far I have not, just ambient and high O2 to date.

Regards,
Tom Barr

Tom, I read someplace (think it was you - not sure) that algae is waiting' lurking for any change in the terms around and when low oxygen occurs, it's like a sign to them that no other competition is out there or there arn't any macrophytes around - then they burst.
Can you explain that? Do you have any other material I can read about it?
Thanks.

I've looked for causal relationships, but have not found any.
I've seen plenty of correlations, but this is due to die off of other organisms, this releases NH4 as well, not just lowers O2 levels.

Algae use O2 to respire as well.
Not enough will have a bad effect on some species of algae I'd say.

Regards,
Tom Barr

Thanks.
Sorry to follow this matter further but I'd appreciate it if you'd elaborate further on that or indicate further reading material so i'll dig in there...

Try Google scholar, algae cultivating methods, techniques etc

It's not an easy search.

Regards,
Tom Barr

Thanks.

Tom,

I'm becoming obsessed with CO2. I have increased CO2 to the point where fish are showing signs of stress, but I'm getting very little pearling, I have small traces of bba. My tank is real close to being clean. I was going to increase the current to increase O2, however will that just cause outgassing ? If I increase the current, but don't break the surface will that help ?

Henry Hatch