Re: CO2

[Thomas Barr <tcbiii at earthlink_net>]

> If plants take in CO2 during the day and take in O2 during the night
> wouldn't it be wise to have barely moving water during the day so that CO2
> doesn't bubble out and powerheads with air injectors turned on during the
> night to infuse O2 into the water?

No. If the water is still then the transport of nutrients and namely CO2
will not occur(or will only too slowly). This happens in still backwaters
and lakes/ponds. Near the surface of algae/plat leaves, pH's of over 10
occur. By adding water movement, this layer is broken up. You can take this
too far obviously but good even current is a wise thing for planted tanks.

A well run tank will have excess O2 beyond that of what is in the air at the
end of the lighting cycle. Adding air/ increasing circulation will help to
drive off this well earned O2 surplus. You want to keep this and hang on to
it. 

If your plants are not producing good O2 levels, then you should try to
figure out why. Then correct that issue.

Folks that insist that they need to add aeration at night/powerheads on
timers have either too many fish for the tank or have not mastered growing
the plants well. They can use this method as crutch till they learn how to
grow the plants better later on. I think the goal of good healthy planted
tanks is the better way to approach the problem. Some may differ.

Plants do not use much O2 at night relative to the bacterial/fish
uptake/outgassing. You are not helping the plants out by adding the O2,just
the fish and the bacteria.
 
> After reading quite a bit of info on CO2 I'm under the impression that it
> causes a PH swing (which I've seen) which is bad and high levels of CO2 can
> cause internal problems with fish.

Why are pH swings bad? Are they unnatural?
Not enough CO2 for the plants when they need it, now that is bad. But pH
swings are not bad per se. Ideally you want to minimize the swings during
the photocycle (this maintains a nice constant level of CO2 when the plants
need it). But I turn my CO2 off at night. The pH swings up etc. So what.
Doesn't effect the fish, it happens slowly, older tanks have less swing, no
difference in plant growth either way(on 24/7 or off at night).

> Wouldn't the optimal amount of CO2 to
> inject be the amount where your plants get only as much as they need.

"When" they need it. More CO2 is okay also, it's the fish/critter population
that set the high range. The more CO2, the better for the plants(up to a
point).

> This
> would result in injecting CO2 but not being able to monitor any change in PH
> or CO2 levels - because your plants are using it all up.

You got it. Uptake = input.
 
> Is there any way to buffer the PH effects of CO2?

KH, baking soda but I think I see what you are getting at here. Don't mess
with the pH. Get the KH up to 3 or higher and then use only CO2 to
manipulate the pH. Don't monkey around with other buffers.
 
> For instance I was as 7.2
> and now I'm at 6.6. 6.6 is fine but when my CO2 runs out I don't want a
> quick swing to 7.2. Gradual would be more preferred."

Again, what do think happens in nature? It will happen gradually in your
tank. Don't let your CO2 run out for too long( a day or two is fine).
pH swings of 6 in the am to 10 in the pm are common in productive
lakes/ponds and pools. More typical swings are about 2 pH units in a 12 hr
period. Variations in rain, location of water inputs etc all can
dramatically alter pH. They do happen relatively slowly. Sudden shocks from
adding 50-70% tap water at 7.9 to a tank at 7 have not shown to be harmful
in my own tanks for many years. Never lost a fish etc due to this.

Outgassing at night is going to be much slower than that.

> 
> Has anyone ever built a system to limit the amount of CO2 coming from a DYI
> setup so that you can adjust your bubble rate without blowing up the yeast
> bottle?

Yes. A couple of methods.
Regards, 
Tom Barr

> 
> Thanks!
> 
> Sam