Adsorbing and Absorbing Medias
In this article we’re going to talk about three chemical filtration medias that are widely used by aquarium hobbyists; Zeo-Carbon, Activated Carbon and Zeolites. We will not only be looking at how these can be used to our advantage but also the dangers of using them.
Absorption and adsorption are two different processes, although fairly similar. When substances are adsorbed their atoms, ions or molecules bond to the surface or pores of the adsorbing media, think of this like iron filings being drawn to a magnet. Whereas with absorption the entire media is used to hold the substance, a good example of this is water being soaked up by a sponge.
Zeo-carbon, as the name suggests, is a mixture of zeolites and carbon. Ammonia doesn’t bond well with activated carbon and therefore will make very little difference to ammonia levels, so the addition of zeolites ensures the ammonia adsorption is to the highest degree. Having said this carbon is the best and most effective way of removing ammonia fumes. However zeo-carbon is not particularly cost affective. This is because carbon has a maximum life span of three weeks in comparison to the six weeks zeolites are active. So theoretically you are paying for zeolites but only getting half of their use. Zeo-Carbon comes in two ways, as loose chips with the materials mixed up together or as a sponge; commonly the sponge is activated carbon with zeolites impregnated in the centre. Both carbon and zeolites have their pros and cons which we’ll look at individually in the following paragraphs.
Activated Carbon is a charcoal based substance that can adsorb certain chemicals and absorb organic matter. There are two processes that can produce activated carbon, Physical Reactivation or Chemical Activation. Carbon is formed from carbonaceous materials such as wood, coal and nut shells to name but a few. Only carbon made from wood or coal are made for use in fish tanks.
The first stage in this process is the material, such as wood or coal, being put through a process called Pyrolysis. Pyrolysis basically means the material is exposed to high temperatures in an oxygen free environment containing argon or nitrogen gases, creating carbon as a result. Oxidizing is the next stage, this involves the carbonized material being exposed to steam or oxygen at high temperatures. The oxidizing process causes many tiny pores to open as a result, producing activated carbon.
Before the material is carbonized a strong chemical such as acid or salt is embedded in to it. After this the material is carbonised by being exposed to lower temperatures in comparison to Physical Reactivation. With Chemical Activation the carbon forming and activating happens simultaneously. This is the preferred method of making activated carbon as it is the quickest and cheapest process.
What You Need to Know
It’s vitally important to replace carbon, or any media containing carbon, every two to three weeks. If carbon is left neglected in the tank or aquarium over a long period of time it can dissolve in to the water, this may very well be one of the causes of lateral line erosion. Carbon will also remove certain vital minerals and can possibly shorten the fish’s life span as a result.
The red line shows where the lateral line is. This is a sense organ that all fish have to detect movement and vibration.
One thing carbon does help with is breaking down organic matter. Heterotrophic bacteria forms in all aquariums but they particularly like carbon to build their colonies around. It’s this bacteria that uses waste as a food source and produces ammonia. Heterotrophic bacteria is both anaerobic and aerobic, this means it can live in both heavily oxygenated water as well as environments with low oxygen. The trouble with Heterotrophic bacteria is it can compete with Autotrophic (nitrifying) bacteria for oxygen and surface space. Heterotrophic bacteria can multiply every 30 minutes whereas Autotrophic bacteria can take 12 to 24 hours. Adding carbon can actually strengthen biological filtration as a result of providing an ideal surface area for Heterotrophic bacteria, which in turn leaves more space for nitrifying bacteria elsewhere in your tank or aquarium. However I would still not recommend long term use of carbon, although it may be worth adding activated carbon on a temporary basis if you’re having trouble starting a cycle. This would give the nitrifying bacteria more of a chance to mutate and build up a stronger colony, especially in an over stocked tank.
The most recommended way to use activated carbon is in emergencies. It’s always good to keep some carbon sponges or chips in your store cupboard. If dangerous medication is present in the water or someone uses hair spray near the tank for example, using carbon combined with water changes will ensure all the toxins are removed. Keep the carbon in the tank for a minimum of 48 hours.
Below is a table of the many toxins activated carbon will remove or reduce.