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Re: pH and CO2 in new tank
On Sun, 30 Jan 2000, Frank wrote:
> After reading the lists for several months, I set up a 70 gallon tank,
> following all the advice I could get. It has been up and running now for
> about 4 weeks. For the most part, everything seems to be doing okay, but I
> do have a few problems which I don't understand. The first concern is Ph and
> Co2. My tap water has a Ph of 6.8 which is what this tank started out with.
> The Kh is 6, and pressurized injected Co2 at about 1 to 2 bubbles per second
> should read about 28 ppm according to George L. Booth's chart on the krib.
If your tap water has pH of 6.8 and a KH of 6 (I'm presuming you mean 6
degrees of hardness) then your tap water is carrying about 28 mg/l of CO2.
CO2 that high is very odd, particularly for a public supply as it's bad
for pipes and tends to cause high metal content in the tap water --
something that state regulators frown upon. That CO2 level is more likely
if you're on a private well instead of a public supply but even then it
would be unusual.
The CO2 level in your tap water (whether or not it's 28 mg/l) has nothing
to do with the 1 or 2 bubbles per second that you are injecting. CO2 is a
gas and it tends to escape from the water. If you don't inject CO2 then
the pH in your tap water should rise to 8 or so. It has nothing to do
with whether your tank is new or old. Another possibility is that you
have something in your tank (shells or carbonate minerals in your
substrate, for instance) that are neutralizing acids in your tap water and
causing the pH to rise.
> However, after testing with a Red Sea Co2 kit, I could not get a reading - no
> matter how much reagent I added, indicating I thought, a very high amount of
> Co2. Thinking the Red Sea kit was in error, I tested with a La-Mott kit.
> Results showed over 100 ppm. of Co2. If I turn off the Co2, the Ph steadily
> rises approaching 8.0, which I do not want.
So what are the pH and KH of the water that tests out to 100 ppm CO2 with
the LaMotte kit? If you have 6 degrees KH and 100 ppm CO2, then your pH
should be less than 6.3. If your pH and KH tests agree then everything is
consistent, but 100 ppm CO2 is a lot to get out of 1-2 bubbles per second.
> The few fish, ottos, barbs, and
> tetras - 10 in all don't seem to be doing well either, In fact, a few have
> died. Can the Co2 be as high as indicated and what makes the Ph in a new
> tank keep rising?
Fish deaths in a new tank are anything but odd. You don't need to call on
high CO2 levels to explain them.
Perhaps there's another explanation for your odd readings. Organic acids
in the water can cause the pH-KH relationship to give incorrect results
for CO2. If you have organic acids in your tap water, then it would
explain the apparent 28 ppm of CO2 in your tap water. In addition, I
suspect (but don't actually know for sure) that CO2 test kits actually
measure a quantity called "acidity", which is analogous to alkalinity, of
KH. If so, then organic acids in your tap water can cause problems for
that measure as well.
If you have enough organic acids in your tap water to cause that much
trouble for your tests then probably your water should be colored. If
you're on a public water supply your best bet is to give them a
call, discuss your test results with them and get a real analysis of your
water supply.
> I change 25% of the water every week, have 200 watts of
> flourescent light, 50/50 mix of laterite substrate, tank is heavily planted,
> and plants are growing, but lately some are turning yellow - especially the
> Ludwigia, the Didiplis Dian,and the Crypt, Wenditi, so I started adding some
> Pmdd. Also, as of yet, have no algae of any kind. Please Help. Frank , West
> Chester, PA.
If you're keeping only 10 fish in a 70 gallon tank then I wouldn't be at
all surprised if your yellowing plants indicated a shortage of nitrogen.
Roger Miller