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got a DIY CO2 rig working fine (bubling continuously) now, but now i came to think of another problem:
should i turn off the airpump?
on one hand, the air bubbles help release the desolved CO2 back to the atmosphere.
on the other hand, i need that oxygen, aspecially at night.
i could disconnect the CO2 rig at night, but that will jerk with the Ph.

should i turn the airpump off while the lights are on?
should i turn it off at night?
should i turn off the CO2 at night instead?

should i turn the airpump off while the lights are on?

Yes.

on the other hand, i need that oxygen, aspecially at night.

Run the air pump at night when the lights are off.

Hi,
The normal CO2 saturation in a tank at equilibrium
is about 5mg/l. Plants seem to prefer something
between 15-19mg/l saturation.

If you use an airstone or a filter return that riles
the surface, then you are breaking the surface tension
that is helping to hold the CO2 that you injected,
within the water. The aeration drives off the excess
CO2 sending the tank back to near equilibrium.

With the ideal CO2 saturated tank, especially one
that is DIY CO2, you don't want airstones, nor do
you want the filter return to be riling the surface.
You want a quiet surface. With Bottled CO2, you can
increase the CO2 injection to compensate for the
agitated surface and still maintain the desired
saturation.

Unless your tank is heavily overstocked, you do
not need to shut off the CO2 injection. Yes,
with the lights out plants switch to using O2 instead
of releasing it, but that effect is way, way over
stated. The only time you NEED to shut off CO2
injection, is if you find the fish gasping at the
surface first thing in the morning. If they are
not doing that, then leave the CO2 injection, and
rate of injection, alone. It takes a while for
the CO2 saturation to build back up to the desired
level after you shut it off, and the tank returns
to equilibrium, and that is just wasting gas.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

with the lights out plants switch to using O2 instead
of releasing it, but that effect is way, way over
stated.

That depends on the amount of plants, does it not? I've seen a tank with a kh of 4 degrees go from a ph of 7.4 to 7.0 an hour after lights off, with no co2 running.

I know of many people that have diy co2 that have an airstone on a timer, set to go on a couple hours after lights out and to shut off a few hours before lights on. I've never used anything besides pressurized co2, but I thought this was the norm for diy people?

[span class="edited"][Edited by jake 2004-08-02 22:22][/span]

Unless you use pressurized systems, no way to shut off the co2. If filter disturbs surface too much you can stick a piece of sponge in the pickup tube to reduce flow. Airstones defeat the purpose of co2.

The Amazon Nut...

So diy co2 people just leave their co2 going all night and don't use an airstone AT NIGHT to outgas it?

Hi,
As I mentioned in my earlier post, there is no sense
in spending the day building up the CO2 saturation
only to rid the tank of it during the night.
That is a needless waste of the gas.

Unlike with a bottled system, there is no way to
shut off the chemical reaction that produces the
CO2 in a DIY system. Plugging the system or using
a valve to shut it off would cause tremendous back
pressure that would result in leaking at weak points
in joints, or explosion of the container. The only
other way would be to shunt it off into the atmosphere
with a valve.

Jake's post does touch on an important value, the KH of
the tank. KH is a measure of the Carbonate Hardness
of the tank's water. In tanks with low KH the pH will
swing over a greater range between hours of light
and hours without light. Between times of CO2 injection
and no injection. The KH buffers the acid (pH) and
the higher the KH, the smaller the pH swings.
This can be a double edged sword however. If the CO2
output drops off, it won't make a "dent" in the pH
if the KH is high. On the other hand, with DIY CO2
the output is "fast and furious" in the beginning,
and with a low KH the pH would drop like a rock at
first, and then slowly climb as the concoction ages
and the production drops off. It's better for the
fish and the plants to have a higher KH.
If your KH is low, simply add regular, unscented,
baking soda to the tank ( a little at a time and test)
to raise just the KH.


If you are using bottled CO2 injection, IMO you should
have a KH of 3 at the very, very, least, and preferably
have a KH around 5.

If, and only if, your fish are gasping at the surface
first thing in the morning, then you need to add an
airstone as the O2 is below the level where they are
comfortable.

Jake also makes comment about the pH shifting .4 within
an hour of lights out in a tank. He mentions nothing
about the surface of that tank and is it being disturbed
by the filter return. Actually, whole lakes shift that
.4 and even more when the sun goes down and the fish in
the lake are perfectly fine with the pH swing.

With a basic bottled system, you have a regulator and
secondary regulator the needle valve. You open the tank,
and then adjust the first stage for about 1bar, then you
adjust the needle valve to deliver a specific number of
bubbles per second. Turning off the system should, for
safety, be carried out by backing off the 1st stage to zero
and then opening the needle valve to allow the exess gas
out, then turning off the tank. That is alot of valve
twisting and can wear out the gaskets, valves, and valve
seats. Additionally, the chances of getting the right
settings the next day, are not very good which means
that you have to "fiddle" with the needle valve for
a while to get back to your origional setting (pH)

What is usually done, is to shut off the gas with a
solenoid valve. This valve is connected to either a
controller, or a timer. If a controller is used, it
also has a pH probe connected to it. The controller
is set so that when the pH raises to a given point,
the gas is turned on, and when the pH drops to a set
point, the gas is turned off - all automatically.

With a timer, the solenoid is turned on with the lights
and off with the lights.

Frank


[span class="edited"][Edited by FRANK 2004-08-03 09:47][/span]

-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--