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Explain this...

ceg4048

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Garuf said:
He says purigen, which is essentially carbon it just doesn't remove ferts.
No, Purigen and Activated Carbon are not the same. The Activated carbon added to the filter is to remove a wide variety of inorganic and organic toxins and the Purigen removes organic nitrogenous wastes.

A lot of people seem to be paranoid about Activated carbon for unfounded reasons. They blame carbon for removing trace elements, which it may do to some extent, but so what? Just add more traces. If you're dosing EI you're always adding more than the plants can use anyway so this is never an issue. Fluval has an excellent zeolite-carbon granule mix that works like a charm. I fill entire trays of my filters with this and I've never suffered any issues with trace deficiencies.

Cheers,
 

ceg4048

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Well theoretically the activated carbon should be changed after three weeks or so. That's because the bonding sites where the unwanted chemicals adhere to on the carbon surface all get filled so no more removal occurs. Activated carbon is highly porous and has a very high surface area because of the way that it's processed. It does not necessarily remove or change the chemicals - they loosely adhere to the carbon surface due to weak intermolecular forces called Van der Waals, which are not actually chemical bonds, just loose bonding due to polarity between the atoms.

In any case since I'm both lazy and a cheapskate I leave it in there for months so I'm not the best example... :oops:

Cheers,
 

aaronnorth

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ceg4048 said:
Well theoretically the activated carbon should be changed after three weeks or so. That's because the bonding sites where the unwanted chemicals adhere to on the carbon surface all get filled so no more removal occurs. Activated carbon is highly porous and has a very high surface area because of the way that it's processed. It does not necessarily remove or change the chemicals - they loosely adhere to the carbon surface due to weak intermolecular forces called Van der Waals, which are not actually chemical bonds, just loose bonding due to polarity between the atoms.

In any case since I'm both lazy and a cheapskate I leave it in there for months so I'm not the best example... :oops:

Cheers,

On TFF, it is said that activated carbon becomes saturated after a few days, then the toxins are released back into the water so it should be removed - not the 3-4weeks like suggested by many. Any thoughts/ knowledge on this?
 

ceg4048

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Tom may have more data, but I just do see any evidence of this. I recall seeing a post recently referencing an article on The Krib showing a fall in Fe concentration over an eight or ten day period with carbon in the filter(?). If this 2-3 day release was valid then that would have shown up in the experiment right? Therefore it's difficult to reconcile these two concepts.

Cheers,
 

aaronnorth

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ceg4048 said:
Tom may have more data, but I just do see any evidence of this. I recall seeing a post recently referencing an article on The Krib showing a fall in Fe concentration over an eight or ten day period with carbon in the filter(?). If this 2-3 day release was valid then that would have shown up in the experiment right? Therefore it's difficult to reconcile these two concepts.

Cheers,

yes, it is a chemist sharing this information so i tend to believe what he writes, here are his posts on carbon if you are interested:
http://www.fishforums.net/index.php?act ... ted+carbon
 

Themuleous

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Well interesting development, I put the java fern from my community tank into this tank (its a lovely healthy plant, just loves the lower light its been under) and this is what it looks like tonight...

P403004.jpg


Sooo much pearling, I know its only one day but this would seem to confirm that the substrate is the issue, as NONE of the plants in the substrate pearl like this ever, even the new ones I added the other day.

Here's hoping the strip down and new substrate does the trick :) boy will I be pleased.

Sam
 

TDI-line

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Finally. :lol: :lol: :lol:

I suppose you could add those heating cables now, with a temperature computer, and i suppose a ph monitor too. :D

I've got some going cheap. :twisted:

But at least you have a way forward now Sam.
 

Themuleous

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Thanks guys, let hope it works!

I'm gonna stick with the akadama, mostly because of the cost. Might sound daft given this experience, but it did work once in my nano, which I didn't pre-soak and James and lots of other people have used it with great results. If it doesn't work again I'll probably try ADA AS but I really don't have the cash for that (dam my huge tank!). It also really has to be a complete substrate rather than a base layer as I want 100% HC and the roots are never very long, so doubt a base would be any use, or I would have gone for tropica with black gravel.

Sam
 

aaronnorth

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ceg4048 said:
Aaron, the link doesn't work for me. Can you summarize?

Cheers,

it was a link to the members post(s), might not work if you arent a member? Not sure.

i'll take a post:

Carbon is fairly unnecessary in my opinion, and even takes away some potentially valuable chemicals in the tank.

First of all, carbon is only truly useful for about a day or two. After that, it has become saturated and really doesn't take up much more. In fact, the bonds between what is adsorbed by the carbon and the carbon itself are reversible, and the potential exists for the adsorbants to be releases back into the tank. So, to really get get the most out of carbon, you have to change it every few days or so.

Secondly, carbon does adsorb a class of compounds called DOCs (dissolved organic compounds, tannins is a very good example). DOCs can actually be quite useful in a fish tank -- DOCs bind to heavy metals, making the heavy metals much less toxic than in their original form. If the carbon is taking away those DOCs, then the metals could be free in your tank. Part of this issue is that the levels of metal toxicity in water for humans can be as much as 1000 times higher than the level of metal toxicity for fish. I.e. copper is not toxic to humans until well back the concentration where the average person can taste copper in the water. But, at that point, the concentration of copper is already many, many times the level of toxicity for a lot of fish. The water companies aren't regulating their water to be safe for fish, they are regulating their water to be safe for humans. If your tank has DOCs in it (some come from the fish themselves, more come from live plants if you have them), the DOCs can bind with copper making the copper much less toxic.

Many water conditioners do bind up with heavy metals, too. But, there is this extra level of protection that activated carbon will take from the water. I think it is a good idea to leave that extra level of protection alone.

I personally only use carbon after a course of medications. The carbon is very good about getting medications out of the water. Then, I throw the carbon away (again, it can release chemicals back into the tank!). And, I too have crystal clear water. Good maintenance and water changes accomplish that more than anything. Carbon is just something extra the manufacturers want you to buy once a week or once a month. It isn't necessary, and has limited benefits in my opinion.

The chemicals that get adsorbed onto the actived carbon are in equilibrium with the tank water. The activated carbon will take up chemcials until that equilibrium is reached. What that equilibrium point is depends upon the concentration of the pollutant and how used up the carbon is already -- what percentage of the active spots on the carbon are still available.

Normally, when using carbon to take out medications for example, it will take up an overwhelming percentage of the chemicals. Say from 100% to 0.1%. What I mean is that 0.1% is the equilibrium. Now, you do a 25% water change. So, concentration of chemicals is now 0.075% in your tank. If you do not change the carbon at this time, the carbon will release some of the chemicals, again going towards equilibrium. Since, most of the chemicals are on the carbon now (99.9% of the original amount) given enough time (and this depends on temp, pH, etc.) the sysytem will tend toward equilibrium again. Meaning the carbon realeases 0.025% back into your water, to bring the concentration of chemcials back to 0.1% -- equilibrium.

Not a huge amount, but you see how a little bit can be released back. And long-term exposure, even at very low concetrations can lead to ill health.


Here is even a little more:

Lets call c the concentration of any chemical in the water that will be adsorbed.

If the adsorbtion at equilibrium follows the Langmuir isotherm (probably the most common -- there are others) the concentration of the chemical on the carbon, which I will call n is equal to:

n = c/(K+c)

K is the called the adsorption or equilibrium constant. It will vary depending upon what chemical we are talking about, and what quality the carbon is.

The total concentration of chemical is T

T=n+c

or using the definition of the adsorbed amount

T = c/(K+c) + c

Now, if we lower c a little (by doing a partial water change, for example) T does get lowered to T2, but so does n -- so call the new n2.

But again, T2=n2+c2 where n2=c2/(K+c2)

where does the difference adsorbed (n2-n) go? back into the water.

The carbon will uptake and release chemicals until equilibrium is reached, every time. So, yes, it is usually a small amount that will get released back -- carbon is very efficient uptaking chemicals when active sites are available -- but a small amount does get released.
 

ceg4048

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Well, was all this in the context of a planted tank?. I mean, plants absorb metals like copper so this isn't a problem. Again, are we to accept the 2 day theory or the data shown on The Krib link? Both cannot be true at face value. If the 2 day theory is correct then the Fe dissipation curve would show a rise every two days as the Fe is released back into the water column - that is unless something else is happening to the Fe not explained, or unless the Fe measurement is faulty (which is a distinct possibility).

It's also not explained how/why the carbon adsorption sites should reverse their hold on the compounds. As discussed, the attraction to the carbon sites are due to polarity attraction. Since there are no changes in polarity why should the carbon all of a sudden release their hold on these compounds? Again, these are not chemical bonds so it's not clear to me what forces should cause release of the compounds unless the local concentration causes the compounds to repel each other off of the adsorption sites. If thats the case then the situation would then reverse itself and low concentration would then result in a renewed attraction to the site and the carbon would adsorb the compounds again. It can't be a one way street unless the carbon sites get clogged with debris so that they are no longer available.

As far as I can see the worst that can be said is that the carbon sites get filled and it becomes incapable of adsorbing any more but the idea that it dumps everything back into the water column - and then doesn't re-adsorb seems a stretch. Maybe there is an explanation but it doesn't seem obvious.

Cheers,
 

GreenNeedle

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If Carbon adsorbs Phosphate and Fe could it not lock the Fe up and therefore if it were to release the nutrient back into the water column the Fe wouldn't register?

I tend to agree with Ceg here though. I think that yes it runs it course pretty quickly and clogs up which is why it is used. For the speed that it removes 'unwanteds' from the water. At which point we remove it.

The manufacturers who virtually all go by the old fashioned 'remove all excess nutrients and metals' would be telling people to remove the Carbon after 2 days if it were true. They are after all in the business of selling to the hardened 'old school' and wouldn't want loads of 'I used Carbon and tested after 3 days. It has done nothing' comments'.

I would suspect most manufacturers actually understand the way all of these items works and also how planted tanks work, but in the interest of selling product selectively choose their marketing statements and in the main suggest the ways that the majority of people most likely to buy their product have always believed in order to maximise sales :)

AC
 
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