how long before carbon is "saturated?"

Trigeek

Trigeek

Member
When using carbon to help clean the water, how long does it take before its usefulness is used up? I've read it gets "saturated" with dissolved organics after a short period of time and could contribute to phosphate levels in the water column. I run activated carbon 24/7 in my sump before the return. My phosphate levels have been 0 for quite a while. I don't want problems.

Is it wise to run carbon 24/7?
Should it be changed often?
How often?

Thanks in advance to all those wiser than me.
 
I change mine once a month, but I don't know of any really strong data on how long the carbon actually lasts. That's vary from tank to tank quite a bit, I'd guess, since it's removing organic compounds.
 
300 gallons-2 cups, setting in one of the overflows. Changed on the 1st and 15th. I was changing only once per month but could see the water clearity decine by months end.

SteveU
 
Yep Steve, seeing is believing.

I always say, if it looks good, it is good.... and if it don't....time to change the plan. :D
 
Thanks everyone. I've been changing every month, too and will keep this regimen until I see it as a problem. My 'ates all measure zero and I want to keep it that way. I posed this question because of some info I saw on another thread regarding activated carbon. It was said that the carbon gets saturated in a very short time (opinions varied from hours to four days). Due to this information, it was recommended to run carbon for short periods. No "proof" was provided, just posters giving information on what they know. I'll keep my carbon practices as is until I see water quality problems, then I'll evaluate the source and consider changing the carbon sooner if needed. Again, thanks for the replies.
 
<a href=showthread.php?s=&postid=10379412#post10379412 target=_blank>Originally posted</a> by Serioussnaps
It takes hours to exhaust a moderate amount....let me find my sources.
Click to expand...

Looking forward to your info, Serioussnaps. I know carbon is beneficial, but if left in too long without changing, is it detrimental? My own anecdotal evidence says no. But that is in my relatively young sytem with a low bioload, macroalgae, good skimmer, 6 inch DSB and water changes every 10 days.
 
The nature of carbon is not only to stop absorbing but to also release after reaching saturation. IMHO anywhere between 2 weeks to one month is good.

I soak all my carbon in RO/DI for 2 or 3 days prior to use to remove ash. Once it is in I knead the bag lightly every day or 2. This prevents water channels from being formed inside the bag.
 
There is no way of knowing how long it will take, there are to many variables.

There is a test you could do to see where you are at and go form there. Take some of the used carbon a put it in the bottom of a bucket with some very mild circulation and add a of drop of Methylene Blue ( LFS medication, a blue dye) or some food coloring that has been diluted with water so the water has a slight color to it when added. Wait a few hrs and see if the color has become lighter and how light it has become.

GAC works more than 2-4 days but it is this time when it is at its max adsorption rate. Every 1-2 wks the GAC should be removed, tumbled in it bag and crushed a little as you do this with your fingers and then rinse it out well. This will rinse out a lot of the stuff that is plugging some of the pores and at the same time open and expose new surface areas. This can extend the life of the GAC where it can still do its job, depending on the type of GAC and the tank itself. 1-2 months is about the max where it should then be replaced.
 
That sounds about right Boomer. I have probably gone thru 500 lbs of activated carbon over the course of many years. I can look at the tank(s) and tell if I waited too long to change the carbon. The water looks "dingy" or yellowish. Within a couple hours of adding new carbon the water looks clear again. I dont think I have ever seen the "dingy" appearance after a week or two, normally it takes a month or so.

Jeff
 
Yah Jeff as you probably have figured out GAC is kinda hit and miss with many variables, i.e., partcile size , type of GAC, how much, filter method, bioload etc. etc...

Yup, me to, probably a dump truck full in 40 years :lol:
 
Piggybacking on this thread - what is the worst that can happen if you have a 150 Two Little Fishies PhosBan reactor filled with GAC from Two Little Fishies, and left it in the fluidised reactor running in a reef for 6 months? In other words roughly 6 times longer than the recommended change interval.
 
<a href=showthread.php?s=&postid=10385857#post10385857 target=_blank>Originally posted</a> by Boomer
There is no way of knowing how long it will take, there are to many variables.

There is a test you could do to see where you are at and go form there. Take some of the used carbon a put it in the bottom of a bucket with some very mild circulation and add a of drop of Methylene Blue ( LFS medication, a blue dye) or some food coloring that has been diluted with water so the water has a slight color to it when added. Wait a few hrs and see if the color has become lighter and how light it has become.

GAC works more than 2-4 days but it is this time when it is at its max adsorption rate. Every 1-2 wks the GAC should be removed, tumbled in it bag and crushed a little as you do this with your fingers and then rinse it out well. This will rinse out a lot of the stuff that is plugging some of the pores and at the same time open and expose new surface areas. This can extend the life of the GAC where it can still do its job, depending on the type of GAC and the tank itself. 1-2 months is about the max where it should then be replaced.
Click to expand...


Thanks, Boomer. The tumbling and crushing routine makes sense. When rinsing the carbon after doing this, should I use water from my ro/di filter or is tap water o.k.? I would think that maybe the carbon would "trap" some stuff from the tap. Any thoughts on this?
 
Last edited:
<a href=showthread.php?s=&postid=10389218#post10389218 target=_blank>Originally posted</a> by Mr31415
Piggybacking on this thread - what is the worst that can happen if you have a 150 Two Little Fishies PhosBan reactor filled with GAC from Two Little Fishies, and left it in the fluidised reactor running in a reef for 6 months? In other words roughly 6 times longer than the recommended change interval.
Click to expand...

My guess from what I've read so far:
1. The carbon would be ineffective in removing anything from the water

2. The carbon may release stuff back into the water

I have trouble with scenerio #2. What breaks the bond between the carbon and the chemicals it adsorbs? I mean the carbon isn't a cup that fills up and overflows when it gets full. It binds (I assume ionic bonds) with the dissolved organics that it removes. Can anyone explain the chemistry behind this?
 
There is both absorption and adsorption going on with carbon. If I remember correctly it was Steven Spote (sp?) who talked about it in one of his aquarium books. While there are others on RC who ca undoubtedly go into the actual chemical process by which it releases much better than I can. I assume certain impurities are more polar than others causing the ones currently bound to the carbon to get "bumped" out of the way or released in some fashion.

Like I said I am sure Randy can explain much, much better. I failed chemistry miserably.
 
GAC is both mechanical and physical filtration and it is more of the mechanical type that can get released. Chemical adsorption is by a process called hydrophobic adsorption which is the same process used by skimmers. Hydrophobic chemistry is an excessively complicated chemistry, that revolves around Van Der Wal's force. In short, hydrophobic substance are attracted to a hydrophobic surface and it is not a very strong bond and some substances surfacers may be from weak to strong.

"Hydrophobic = When nonpolar molecules tend to form intermolecular aggregates in an aqueous medium ."

Thermodynamics

The hydrophobic effect can be nullified to a certain extent by lowering the temperature of the solution to near zero degrees Celsius; at such temperatures, water tends toward an ordered structure and the order generated by hydrophobic patches is no longer as energetically unfavorable. This is neatly demonstrated by the increased solubility of benzene in water at temperatures lower than room temperature.

The transfer free energy of nonpolar molecule from nonpolar solvent to aqueous solvent is often used to quantify the hydrophobic effect. The transfer free energy of hydrophobic molecule, Ã"žGt, is positive. The Ã"žGt can be decomposed to the enthalpy component Ã"žHt and entropy component − TÃ"žSt by the thermodynamic relation G = H − TS. In room temperature, Ã"žHt is approximately zero, and Ã"žSt is negative. In other words, the hydrophobic effect is entropy driven at room temperature. The other characteristic thermodynamic quantity of the hydrophobic effect is heat capacity change in transfer, Ã"žCp,t, which has a positive value as contrasted to a negative value in the transfer of a hydrophilic molecule.

Another way of understanding the hydrophobic effect is the example of a hydrophobic substance in water. Pure water molecules adopt a structure which maximizes entropy (S). A hydrophobic molecule will disrupt this structure and decrease entropy, and creates a 'cavity' as it is unable to interact electrostatically with the water molecules. When more than one 'cavity' is present, the surface area of disruptions is high, meaning there are less free water molecules. To counter this, the water molecules push the hydrophobic molecules together and form a 'cage' structure around them which will have a smaller surface area than the total surface area of the cavities. This maximizes the amount of free water and thus the entropy.

The Hydrophobic Effect
http://www.cryst.bbk.ac.uk/PPS2/projects/day/TDayDiss/HydrophobicEffect.html

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/hydropho.htm


A better intro
http://www.lsbu.ac.uk/water/phobic.html


The Hydrophobicity of Skimmers
What is Skimming?
http://reefkeeping.com/issues/2006-08/rhf/index.php
 
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