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CO2 at night

>From: George Booth <booth at hpmtlgb1_lvld.hp.com>
>Date: Thu, 20 Mar 1997 08:12:07 -0700

>> I am continuing to dose CO2 from a yeast reactor with a ph around 6.5,
>> happy fish, bubbling plants and my tetra CO2 test measuring ideal
>> levels of CO2.  Do most people turn off the CO2 supply at night?.
>Many do but they (and you) probably should not. 

I agree with George. 
I always believed that a really slow flow CO2 system could run continuously,
but only recently realized that it also applies to a higher (but constant)

For the past few years I have injected CO2 into two of my tanks.... I
started the first over 5 years ago ... a manual system using a pressurized
tank, bubbled into a canister filter. A more recent system uses a
controller. (OK, I am not counting the yeast systems that I also
experimented with but am not currently using... although I still
periodically set one up for special needs). The original manual
(semi-automatic?) system was set up with a solinoid which shut the flow off
at night... at the time, I thought this was an important safety feature to
reduce the chances of having too much CO2.  This approach does require a CO2
safe check valve or the water _WILL_ back up into the CO2 line. 

Recently I tried to split the system using a "T", together with a cheap
metering valve and had alot of trouble getting the flow to stay balanced
between the two tanks. I eventually added a better valve and now control the
flow to two tanks off one CO2 system. Initially, I did not add a second
check valve and at Karen Randall's suggestion, I decided to remove the
solinoid so I could keep the system under positive pressure and quickly
elimate the water backing up at night. During this time, I was checking the
pH in the morning and evening. The system was still not balanced properly,
so the flow rate was quite variable. I think the two tanks were competing
with each other. Despite the uneven flow rate, the pH swings were much less
than I expected. The pH would increase during the day.... some days to 7.0,
others 7.4... it all depended on the starting point. In the morning it would
be ~0.2-0.4 lower. The fish did not croak (dwarf cichlids and tetras). The
plants did not complain either. In fact, the plants in tank that was getting
the CO2 were growing so fast, you could almost watch them grow. (BTW, this
was a tank that had been growing for 4 years without CO2, got a yeast system
a few months ago when its growth started to decline.... the yeast CO2
started to improve growing conditions.) Now, I need to lower the CO2 to get
the result I want.  I finally added a second fine adjustment metering valve
and have better control. I am still fiddling, but the pH swings are smaller
and much more predicable. Diurnal variation is ~0.2. 

Please don't ask me about my KH. I don't test it. All I can say it is that
it is pretty low and is probably lower than it should be. The total
alkalinity of my tap water is 20 mg/L (measured as CaCO3). This is a little
over 1 KH. I do biweekly water changes 20-25%, and I only occassionally add
KH building substances: CaCO3 (one 1500mg Calcium tablet per 70 gallons =
~0.3 KH) and 1 tsp Sodium bicarb (=~0.75 KH); together this raises my KH
around 1 unit. My guess is that the KH probably stays between 0.5-1.5.
Generally low by usual standards, but it has been 'good enough' for me. I
prefer small changes to my chemistry, so if I move fish to different tanks
or stop adding CO2, there will not be a big change. I also like to limit the
plant growth <g>.

George also says that
>Since it
>is difficult to accurately measure small quantities of dry chemicals
>at home, a test kit should be used to verify the actual KH and GH that
>is achieved.

I have to disagree on this one. This measurement of dry chemicals is NOT
difficult for what aquarists should have in mind. I think the measurement
skill for making a cake is sufficient for adding sodium bicarbonate to the
aquarium. And whole calcium tablets are pretty easy <g>. Once dissoved in a
liter of water, you can decant any amount. I do agree that actual KH
measurement is needed to achieve a precise CO2 level. But there is a wide
range of acceptable values. I am quite happy with minimal amounts, but to
each his own.

Neil Frank      Aquatic Gardeners Association         Raleigh, NC
      The Aquatic Gardener - journal of the AGA -  now in its seventh year!!