[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: CO2 levels

> From: "Davy Cleys" <davy.cleys at skynet_be>
> Subject: 3rd posting: CO2-levels
> This is the third posting of the same message... still hoping to get some
> reaction (almost giving up on it). With all the expertise on this list, one
> should expect to get some answers...

	Maybe no-one had any good ideas....  :)

> > First of all, at the time of the measurement, my tank had a pH of 6.84
> > (measured by pH-elektrode calibrated only a few days ago) and a KH of 4.0
> as
> > measured by the Tetra KH test kit (instead of the recommended 5 ml of
> water,
> > I used 10 ml of tank water, so the KH should be accurate within 0.5
> units).

> > Now, here goes:
> >
> > (1) Judging from the pH, KH and CO2 chart, my CO2-levels are in a range
> > between 17 and 19 mg/l. Right?
> >
> > (2) However, according to the Tetra CO2 test kit, my CO2-levels are
> between
> > 34 and 38 mg/l. (For those who don't already know, the Tetra CO2 test kit
> > works as follows: 20 ml of tank water, 5 drops of test reagent 1 and then
> > count the number of drops of reagent 2 until there is a slight pinkish
> > coloration. To
> > determine the actual CO2-level, one has to double the number of drops of
> > test reagent 2. In my case resulting in a CO2-concentration of 34 - 38
> > mg/l.(17 to 19 drops of reagent 2))

	You have three tests there, giving inconsistent results.  The one that
I would suspect first is the CO2 test.  It must necessarily be pretty dilute
alkali solution, and as such liable to further effective dilution (actually
partial neutralisation) by absorption of atmospheric CO2.  It is just the
sort of standard solution that one does _not_ want to use, and certainly
one that shouldn't be kept very long at all.  In an analytical lab, I
wouldn't trust it beyond a few days.  If it's diluted, the readings go up...

Paul Sears        Ottawa, Canada