There are a variety
of pollutants dissolved in any aquatic environment containing biological
life. Dissolved ORGANIC compounds (DOC's) include proteins, amino acids,
phenolic compounds, pheromones and other metabolic byproducts which
are continuously being exhausted into the aquarium water by the fish
or other aquatic animals. If these organic substances are allowed to
become concentrated, they will negatively impact fish feeding rates,
growth rates and reproduction rates, they will lower immune system activity
and promote blooms of pathogenic bacteria in the water.
These DOC's can be controlled by water changes, however a pretty rigorous
maintenance schedule is required. I recommend maintaining your nitrate
levels at less than 10 ppm (the less the better) since doing so will
concurrently facilitate a low level of DOC's, something which you cannot
test for. THE PROBLEM is that a great many aquarists don't adhere to
such a maintenance schedule and don't test for nitrates.
If you are not managing your nitrates and thus your DOC levels, chemical
filtration is perhaps the best method for you. Carbon filtering removes
DOC's via adsorption. As the aquarium water flows through the carbon
medium, the Dissolved Organic Compounds come into contact with the surfaces
of the carbon granules where they become attached. This is ADsorption
--- not ABsorption. Some DOC's are adsorbed directly, whereas others
combine chemically with already-captured substances. When the surfaces
of the carbon become saturated, it stops working and needs to be replaced
with new carbon.
There are many types of carbon sold for aquarium
use but VERY FEW of these are actually capable of adsorption in water.
Only HIGH QUALITY ACTIVATED GRANULAR carbon which has been degassed
in an oxygen oven at temperatures close to 2,000 degrees Fahrenheit
is functional --- anything else is worthless. I can recommend
Marineland activated granular carbon in this regard though there may
be others. Degassing enlarges the apparent surface area of each carbon
granule, thus greatly increasing the adsorptive capacity.
Look for activated carbon which is phosphate free. a great many carbon
grades are washed with phosphoric acid in an effort to support the adsorption
sites since this is cheaper than degassing. This phosphate will leach
into your aquarium water and can result in a major algae problem.
Deep beds of Granular Activated Carbon (GAC) are always more effective
than shallow ones of equal area. Also, for a given amount of GAC the
smaller the granules, the greater the adsorptive capacity. Generally,
there needs to be 4 to 10 grams of GAC for every gallon of water
depending on stocking density. Such carbon beds typically last only
a month at best and more typically 2-3 weeks since most hobbyists tanks
If your filter uses prepackaged cartridges containing
carbon, realize that these cartridges typically contain poor quality
carbon and if quality carbon is used, only 20 percent or less of the
recommended amounts of GAC is present. You can slit open the
cartridge and fill them with more GAC but many pad filter types simply
will not hold that much. Thus, the carbon in the vast majority of filter pads on the
market simply are is functioning. Therefor why pay for it.
In a filter, the GAC should always be placed after the mechanical filtering
medium otherwise, the particulates in the water will quickly coat the
surfaces of the GAC, rendering it useless.
So what's the bottom line? if you're going to use activated carbon,
you've got to use QUALITY material, you've got use ENOUGH of it to work
and you've got to CHANGE IT often enough to keep it functional. a weekly
water change schedule tailored to your bioload will work equally well
however and is certainly less expensive.