Description
This article is from the Beginning
Fishkeeping FAQ, by Thomas Narten with numerous contributions
by others.
39 Raising and Lowering pH
One can raise or lower pH by adding chemicals. Because of buffering,
however, the process is difficult to get right. Increasing or
decreasing the pH (in a stable way) actually involves changing the KH.
The most common approach is to add a buffer (in the previous section)
whose equilibrium holds the pH at the desired value.
Muriatic (hydrochloric) acid can be used to reduce pH. Note that the
exact quantity needed depends on the water's buffering capacity. In
effect, you add enough acid to use up all the buffering capacity. Once
this has been done, decreasing the pH is easy. However, it should be
noted that the resultant lower-pH water has much less KH buffering
than it did before, making it more susceptible to pH swings when (for
instance) nitrate levels rise. Warning: It goes without saying that
acids are VERY dangerous! Do not use this approach unless you know
what you are doing, and you should treat the water BEFORE adding it to
the aquarium.
Products such as ``pH-Down'' are often based on a phosphoric acid
buffer. Phosphoric acid tends to keep the pH at roughly 6.5, depending
on how much you use. Unfortunately, use of phosphoric acid has the BIG
side effect of raising the phosphate level in your tank, stimulating
algae growth. It is difficult to control algae growth in a tank with
elevated phosphate levels. The only advantage over hydrochloric acid
is that pH will be somewhat better buffered at its lower value.
One safe way to lower pH WITHOUT adjusting KH is to bubble CO2 (carbon
dioxide) through the tank. The CO2 dissolves in water, and some of it
forms carbonic acid. The formation of acid lowers the pH. Of course,
in order for this approach to be practical, a steady source of CO2
bubbles (e.g. a CO2 tank) is needed to hold the pH in place. As soon
as the CO2 is gone, the pH bounces back to its previous value. The
high cost of a CO2 injection system precludes its use as a pH lowering
technique in most aquariums (though see the PLANT FAQ for inexpensive
do-it-yourself alternatives). CO2 injection systems are highly popular
in heavily-planted tanks, because the additional CO2 stimulates plant
growth.
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aquaria, fish, acquarium, tank, fishkeeping
