Activated Carbon

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1 About Activated Carbon
2 What does it do
3 How long does it take to work
4 Can I leave it in the tank
5 Can I recharge it
6 Pictures
7 Links
8 Commercial products

[edit] About Activated Carbon

Activated Carbon (AC) is a charcoal substance which is used in the aquarium to removed chemicals from water.

It is often supplied as a black sponge or as small black beads which is used in filters to remove certain chemicals from the water.

Activated carbon is made of either coal, wood or nut shells (Coconut, etc.) charcoal. For use in the aquarium, only coal or wood based charcoal is used; coconut based charcoal is used for cleaning chemicals from gases.

The sponge is typically placed where there is adequate water flow and manufacturers recommend replacing it after a 2-4 weeks.

[edit] What does it do

Sellers of activated carbon are often vague about the benefits. Terms like 'clean' or 'polish' the water are often stated without actually saying what it does.

Whilst it does trap particles if used in the filter as a foam or beads so does a plain piece of sponge. It does remove some smelly organic gases like Hydrogen Sulphide from the water, absorbs Chlorine from water and small amounts of chelated Copper and Iron may be removed and so may be of limited use.

Once very popular in the 1980s, it's use is better understood in the 21st Century and it is less used today by experienced aquarists.

It is probably overused by the beginner as it is commonly supplied with new filters and aquariums by manufacturers by default and users are often advised to replace it every month. This is probably a needless monthly expense if the tank is new and the tap water is already pre-treated with a water conditioner.

Users should remove the carbon from the filter if adding medical liquids to the tank as it may absorb them.

Constant use of activated carbon is not advised for aquariums with plants.

[edit] How long does it take to work

Activated carbon quality varies enormously, there are cheap and expensive products on sale all claiming to work wonders. But some studies (see The Krib Keslar article) show that in fact that 90% of the absorption work of a piece of carbon in a good water flow in fact occurs within the the first 48 hours and after 100 hours (4 days) can be removed. (Would people buy it if they knew it only lasted a few days?)

[edit] Can I leave it in the tank

Activated carbon will not leak the chemicals back out regardless of how long you leave it in the water. However statements by companies like Seachem do say that all forms of activated carbon do leak out amounts of phosphate. What differs between products is this amount. This may contribute to the development of algae in your tank.

Of course the carbon foam rapidly becomes home to your biological nitrifying bacteria filter. In a new tank in the middle of nitrogen cycle the carbon should never be removed for at least 40days to ensure the cycle is fully established.

[edit] Can I recharge it

Yes and No. Once activated carbon has absorbed its chemicals, it should be thrown away when no longer needed.

It is possible to heat activated carbon to 200°C for 30 minutes. But this will only destroy the organic elements it has absorbed. Any metals will still be present.