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Re: C02 Measurements (long answer)

"II, Thomas Barr" wrote:

>How big is the aquarium first off? Concentrations, age of the peat moss and
>quality, water changes and frequency, bacterial explosions from a new
>nutrient being introduced that lend themselves to producing chemicals that
>lower the ph(?)(not the peat by itself), quality of of the test kit/probe
>problems, yeast/CO2 production based on temperature reduction/increases
>would cause fluctuations, Kh levels changing from source tap water during
>seasonal fluctuations yada yada yada........

Wow, is that one question ? Lets go by parts:

- aquarium size: 46 gallons
- concentrations: NO3-less PMDD and fish food are the only chemicals added.
                  pH 6.4/6.6 (morning/evening with no peat).
                  NO3 ~ 5 ppm, PO4 < 0.1 ppm
                  kH ~ 5 - 6, gH ~ 7 - 11 (with no peat). Slowly increases
                  in between water changes due to something in the substrate. 
                  I'm experimenting with peat to try to control this tendency.
- peat: fine ground sphagnum straight from a fresh bag from the garden store.
        can't recall the brand. Replaced about 200 ml of loose peat in a 
        filter bag every few days.
- water changes: 30% to 50%  every two weeks.
- bacterial explosions: none visible, water is always crystaline. Algae-free
  tank except for some green spot algae in older leaves.
- quality of test kit: pH can be easily read to 0.1 precision (note that
  accuracy is not relevant since we are talking about relative changes).
  kH from Tetra test, used with double resolution (10 ml sample).
- yeast CO2, about one large bubble every 10 sec. About two months before 
  starting use of peat I stabilized gas production by keeping the yeast 
  bottle in a water bucket with a heater/thermostat set to 80 F. Seems very 
  stable, and it's easy to spot the increase in pH when the yeast reaches
  exaustion. I worked this out carefully before starting the peat experiment.
- I measure tap water about once every two months and it is always kH = 4.0,
  gH = 5.0, and pH = 7.4 (for about one year now).

In summary, conditions in the aquarium have been pretty stable for several
months. I throw some peat in, and bang ! the pH drops and the kH doesn't
change. So if I blindly apply the Ph/Kh/CO2 relationship, I would conclude
that CO2 jumped from 40 ppm or so to well above 100 ppm. This obviously
didn't happen, so I conclude then that peat throwed the Ph/Kh/CO2 relationship
out of whack. I also could conclude that this particular peat wasn't good in
decreasing alkalinity but very good in releasing acids, thus the observed
pH drop which has no relationship at all with added CO2. 

-Ivo Busko
 Baltimore, MD