Beverly's Pet
Center FishTalk #2
Carbon Confusion
While browsing the shelves
of most fish stores, you find a multitude of products to condition water. One
of the most useful products is activated
carbon. There are many brands of
activated carbon that vary in appearance and price. What are the
differences? How is it used? What
function does it perform? These are the questions we will answer.
First we'll start with a
little background information on what carbon is. Following the background we'll
cover some guidelines on the use of carbon. We'll finish with the effects of
carbon filtration.
There are many types and
grades of carbon. Activated carbon is made from coal, wood, nuts and even
animal bone. A process of heating the material at high temperatures and then
repeating this in the presence of steam, air or carbon dioxide. Variations in
the processing method yield activated carbons with different characteristics
and pore sizes. These will determine what types of compounds the activated
carbon will filter out. Many
characteristics affecting
the choice of a carbon cannot be readily distinguished by the user. We must
find a good brand, where the manufacturer has done its homework, that has
properties aimed at the needs of the aquarium. Some companies will buy whatever
is cheapest, regardless of its qualities. These are the ones to avoid. Often
companies rate their carbons with names like "hobbyist",
"professional" and "research" grades or "activated"
and "super activated". The better rated carbons cost more and usually
perform better.
There are several observable
traits that can be used to compare carbons. Some carbons have greater volume
for a given mass (in other words, they are lighter or the same amount by weight
will fill a larger container) than others. This indicates more or larger pores
and greater internal surface area. Greater surface area is desirable because it
increases the capacity of the carbon.
The
proper carbon for aquarium filtration should have a dull look and be firm, but
crushable. The inside of the grains should contain a lot of space. You can test this by throwing some activated
carbon into water. The carbon should float for a second and make a hissing
noise before sinking.
Large pore size will trap
large molecules more effectively (organic waste - proteins). Small pore sizes
trap small molecules better. In aquarium filtration we need to remove both
large and small molecules, so an activated carbon with a mixture of pore sizes
is best.
The quantity of carbon that
should be used and how often to change it is not an easy question to answer.
The amount and types of filtration being used are one factor in this equation.
Biological load (amount of fish, feeding, decaying matter, etc.) is also a
major factor for determining the correct amount of activated carbon. Since
actual measurement and calculation to try and figure out the answer would be
quite technical, involved and require expensive equipment, we will take another
route.
There is a large variance in
recommendations for the amount of activated carbon to use and how long to use
it. My recommendation is to use about 10
ounces of activated carbon for each 50 gallons of water and change it every
30-60 days. The activated carbon should
be placed in the filter system so water cannot flow around it, but must pass
through the carbon. This is just a starting point and should be used along with
the information that follows and a little experimentation to find the optimum
usage for your system.
One definite indicator that
the carbon needs to be changed is the yellow tint that aquarium water will take
on over time. This color change may be
difficult to detect in the tank until it is severe. A simple way to check is to
take a little tank water and put it in a clear glass. Hold the water sample in
front of a pure white piece of paper.
This will easily reveal any color.
There are two main factors
causing activated carbon to become inactive carbon Over time the pores in the
carbon become filled with the types of compounds they attract. Once the pores
fill, the carbon can no longer hold any more.
The
second factor causing a decline in the effectiveness of carbon is coating. A
slime type coating occurs on the outside of the carbon grain blocking the
pores. Washing can remove some of this and bring a little more life to the
carbon
At last we come to the final
and most important question "What does filtration with activated carbon
do?". Activated carbon removes many metals from the water. It also removes
dyes and antibiotics. This is why most medications require the removal of
carbon from your filter to be most effective. Good carbon filtration makes the
water crystal clear. This is one of our aims in using carbon but we must not
let it fool us. Don't stop doing partial water changes just because the water
looks great!
A very important function of
activated carbon is the removal of
dissolved organic carbons or DOC. This term lumps together most organic carbon compounds that
are dissolved in water including carbohydrates, proteins,and fatty acids.
Buildup of DOC reduces the
natural buffering ability of water. The explanation of this occurence is very
technical and beyond the scope of this discussion. (If you are interestedin the details, check
out the books referenced at the end of this article.) The bottom line is pH begins to drop and
becomes difficult to stabilize.
Removal of DOC helps the water maintain higher
alkalinity, thus making it easier to keep pH in the proper range.
It is good news that activated carbon removes all
this bad stuff, but unfortunately there are good nutrients that also are
removed. Many trace elements, which are especially vital to invertebrates, are
filtered out of the water by activated carbon. Some suggest intermittent use of
activated carbon in reef tanks. Discontinue use immediately after water changes
or the addition of trace elements. This allows the inhabitants of the tank to
get what they need. The final determination of what is right for your tank must
come from observation. Watch the condition of the water and it's occupants to
find out what works best for your system. Every tank is a unique environment
and I think this is what makes the hobby so fascinating.
References
Moe, M.A. Jr. 1982
The Marine Aquarium Handbook - Beginner to Breeder. Green Turtle Publications.
Plantation, Fl, USA. 170 pp.
Moe, M.A. Jr. 1989
The Marine Aquarium
Reference - Systems and Invertebrates.
Green Turtle Publications. Plantation, FL, USA. 507 pp.
Spotte, Stephen H. 1970
Fish and Invertebrate
Culture: Water Management in Closed Systems. Wiley-Interscience. New York, N.Y.
145 pp.