agd@homxb.UUCP (A.DEACON) (03/08/88)
Ken-
There are several ways to approach your questions. First,
respiration by animals and plants produces free CO2. This causes
a decrease in pH. Some bacteriological processes are
oxidative and produce acids, whereas others, like denitrification,
result in a rise in pH. Plant photosynthesis is also reactive,
causing an increase in pH.
Biological oxidation in aquariums exceeds reduction overall,
and there is therefore a gradual decline in alkalinity and pH.
Mineralization of organic carbon compounds and nitrification
account for the bulk of acid forming processes of bacteriological
origin. Strictly speaking, the end result of nitification
is nitric acid rather than nitrate ions. The result is a reduction
of buffering capacity of the water.
When calcareous gravels are used to buffer a marine system,
the water eventually equilibrates at about pH 7.5, which is below the
recommended level. Regular water changes and sodium carbonate (Na2CO3)
or sodium bicarbonate (NaHCO3) are used to keep pH values up.
The gravel in the tank, over time, becomes less effective in
buffering. It becomes necessary to change out portions of the gravel
when the tank reaches the equilibrium mentioned above. Do it a portion
of the gravel at a time so that you keep a healthy number of bacteria
behind for nitrification.
Many reef systems have areas where the water trickles trough
a shelf or two of crushed coral or crushed oyster shell. The shelves
are easily removed and the buffering agent refreshed.
So to answer your questions:
1. Yes everybody has trouble with pH in marine tanks.
2. Change the water and gradually change substrate or add filtering
material.
3. Salt does increase buffering capability temporarily.
4. I do believe that water changes are necessary, even in
reef systems.
5. Yes, that was a long sentence.
If you have follow up questions or comments, let me know. I have lots
more information available on this topic.
Art Deacon
ihnp4!homxb!agd