Koi Fish Information Centre

This message will be best viewed in HTML so I can bore you properly with a bunch of formulae. These are from Stephen Spotte (1979) who got them from Weber and Stumm (1963)

These formulae all relate to chemical reactions that can affect the pH of your water. This is not to say that any or all of these reactions are occurring at a given time, but they do occur.

Process Reaction Effect on pH
Photosynthesis
6 CO2 + 6 H2O à C6H12O6 + 6O2
increase
Respiration
C6H12O6 + 6O2 à 6 CO2 + 6 H2O
decrease
Methane fermentation
C6H12O6 + 3 CO2 à 3 CH4 + 6 CO2
decrease
Nitrification
NH4+ + 2 O2 à NO3 + H2O + 2 H+
decrease
Denitrification
5 C6H12O6 + 24 NO3 + 24 H+ à 3 O
CO2 + 12 N2 + 42 H2O
increase
Sulfide oxidation
HS- + 2 O2 à SO42- + H+
decrease
Sulfide reduction
C6H12O6 + 3 SO42- + 3 H+ à 6 CO2
+ HS- + 6 H2O
increase

As you can see, there is much more going on n the aquarium than the nitrogen cycle we talk about so much. Those reactions that are reductive tend to increase pH while those that are oxidative will decrease pH. Oxidation happens more than reduction, so there is a general decline of pH over time. Your water changes will combat this tendency for the pH to go down, but, unless you regularly do massive water changes, greater than 25% per week, the trend will still be downward. This is why it is important to periodically check your pH. You can then determine when some large water changes are needed as your pH tends to be lower.

Certainly, there are other factors at work here. Decorative items used in the aquarium can release acids or bases to affect the pH. Waste, be it from fish or plants, left in the aquarium will start to deteriorate, which will then speed up the acidification of your water. Using CO2 to help grow your plants will tend to acidify the water, and this is why many use pH to govern the addition of CO2 to their tanks.

And, we have not even entered the discussion of DOC’s (Dissolved Organic Carbons).

One may wonder why all this happens in our tanks, and not in nature. Well, it does happen in nature. The effects, however, are much less noticeable because of the volume of the water, and other factors that help to negate the effects.

\Steve//

Category: Philippines Internet Koi Society