I have seen a lot of things on the internet boards that leads me to believe that people think that carbon adsorbs Phosphate and then later re-releases it. This isn't true. The carbon came with the Phosphate already in it. (Remember that ANYTHING alive has phosporus in it....Carbon was once a tree that was living....hence the Phosphorus). Luckily, most Carbon's are acid washed now so it's not as big a deal as it used to be.
The time that the carbon releases the most Phosphates is when it's brand new. Soaking it in RO/DI water will remove most of the Phosphates fairly quickly if it's a good brand of Carbon. Even Leo Morin, the head chemist for Seachem recommends doing this.
http://www.hallman.org/filter/carbon.html Quote:
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In terms of ash and phosphate content, acid washed carbons are better than non-washed carbons. Acid washed carbons have had much of their ash and phosphate washed out. Ash is important because it is responsible for "pH shock". Some carbons can increase pH to over 10 in a very short time. An acid washed carbon will barely increase pH to 7 over several days. Carbons that do not alter pH are usually the same carbons that will not leach much phosphate. Ash content may be available on the label, but sometimes it is unreliable. The store owner may be familiar with what the carbon does to pH.
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I think the benefits far outweigh the risks, particularly in non-reef aquaria. Even in a reef aquarium, it is possible to use carbon and minimize the risk by selecting the right carbon and pre-soaking it in DI water for several days to leach out the majority of the leachable phosphate. |
Most carbon sold for hobbiests has gone up in quality in recent years but there is still a difference in effectiveness. See these links
http://www.pets-warehouse.com/carbon.htm http://www.pets-warehouse.com/carbon_1.htm
Activated carbon is used in the food industry, chemical industry, etc. because there is a method of things getting inside small pores.
Viscous Entrainment occurs naturally with both GAC and Live Rock. We like the more porous live rock because of it's increased potential for biofiltration. We like the more porous GAC because of it's increased potential for filtering as well. I don't want to get too complicated here because fluid dynamics are difficult even for scientists. Here's the basics on how carbon works. A single pound of activated carbon has the surface area equal to 125 acres. Very porous stuff. It has been baked in such a manner as to create all of the different types of pores and surface area. Quotes are from Calgon who supplies much of the Carbon sold in America.
http://www.calgoncarbon.com/resources/faqs.cfm#one Quote:
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TRANSPORT PORES---Transport pores are the internal volume of the carbon granule where the graphitic plates are far apart or the cracks and crevices of the particle. The transport pores act as the "highways" for the contaminants to reach the adsorption pores where they are adsorbed. It is important to note that no adsorption takes place in the transport pores. Transport pores are vitally important, as they allow access to the adsorption pores - especially those deeper within the carbon granule.
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Basically the bigger holes.
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ADSORPTION PORES---Adsorption pores are the internal volume where the graphitic plates are very close together creating a higher energy. Higher energy is important to adsorption because it is the energy that "holds" the contaminant (the carbon "adsorbs" the contaminant). The volume where the graphite plates are far apart and the cracks and crevices make up the transport pores. It is important to note that all adsorption takes place in the adsorption pores and not the transport pores.
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Basically the smaller holes.
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VAN DER WAALS FORCE---There is a natural attractive force between all things in the universe. Gravity is one of these forces. In adsorption theory, the force between the contaminate and the carbon is the adsorptive force. It technically is a Van der Waals force. It is this attractive force that enables adsorption to occur. The forces are a function of the distance between the two objects. The closer together the objects are, the higher the attractive force is. The higher the attractive force, the higher the "energy" level of the pore space.
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Basically, this is how Phosphates are adsorbed onto LR (and into LR). Van der Waals forces are exactly how a protein skimmer works as well.
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HOW DOES CARBON BIND THE CONTAMINATE----Once the contaminant enters the carbon granule via the transport pore space, it diffuses into the carbon matrix until it enters the smaller pores where the adsorptive forces begin to take effect. Once it reaches a higher-energy area, it can no longer migrate (or diffuse) because the adsorptive force is stronger than the diffusional force. The contaminant is adsorbed to the carbon surface by the adsorptive forces (the Van der Waals forces). In this state, the contaminant is referred to as the adsorbate.
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http://www.chemguide.co.uk/atoms/bonding/vdw.html (Van der Waal forces)
http://www.marineland.com/articles/16ActivatedCarb.asp http://www.marineland.com/articles/17RevisActCarb.asp
Ok....if you're not sufficiently bored yet, here's the bio-film explanation.
If you add a piece of LR to your tank, the bacterial population will expand and cover every surface of that LR. If it is porous LR, the bacteria will even grow on the inside. They create an invisible, to the naked eye, film called biofilm. For those so inclined, here's your link.
http://www.erc.montana.edu/CBEssenti...bbasics-01.htm
A bacterium really isn't a picky critter. It just wants a house and it wants to eat. It doesn't take too long for them to find a house AND food in your Carbon. They will create a biofilm covering the adsorption pore spaces rendering them useless in a very short period of time. (One to two week max.)
If you leave the Carbon in longer, what's going to happen? Nothing good IMO. The Carbon is covered by a biofilm so it is no longer doing its job at adsorption. Bacteria are thrilled to death that they have a food source. Unfortunately, the life span of most bacteria is measured in hours and not years. They will eat the nasties that were chemically bonded to the Carbon and then die, thereby re-releasing that nasty (including Phosphorus).
That's why I use smaller amounts of Carbon, soak it in RO/DI water, and change it out often.
How often do you change your carbon? 
This has to be the motherload of carbon posts. Thanks a lot inwall for your effort!!! 
