How often to change carbon
- Thread starter bucfan
- Start date
It is impossible to say when to change GAC because we cannot measure what GAC is adsorbing. I am probably going to start using methylene blue to decide when to change it. Here is how.
New GAC adsorbs 5-6 drops of 0.5% methylene blue. New GAC can completely adsorb 1 drop in under 5 minutes. GAC that had been in use for ten days did not adsorb 1 drop methylene chloride even after 20 minutes.
I have no idea what the correlation is between the ability to adsorb organics from aquarium water versus methylene blue, but I think it is safe to say there is. My plan is to do a couple more tests on GAC in use for 1 day and 5 days, then decide how to "call" when GAC is exhausted. I might use the criterion of adsorption time of methylene blue takes twice as long as fresh GAC or that it adsorbs less then 3 drops.
I bought 20 ml of methylene blue on line for $6.
New GAC adsorbs 5-6 drops of 0.5% methylene blue. New GAC can completely adsorb 1 drop in under 5 minutes. GAC that had been in use for ten days did not adsorb 1 drop methylene chloride even after 20 minutes.
I have no idea what the correlation is between the ability to adsorb organics from aquarium water versus methylene blue, but I think it is safe to say there is. My plan is to do a couple more tests on GAC in use for 1 day and 5 days, then decide how to "call" when GAC is exhausted. I might use the criterion of adsorption time of methylene blue takes twice as long as fresh GAC or that it adsorbs less then 3 drops.
I bought 20 ml of methylene blue on line for $6.
Very interesting. I have more Q's then this but....
do you use carbon in a reactor?
Do you plan to use carbon in a special way to be able to test?
Will you isolate the carbon so the dye test can more easily be conducted?
how much carbon per x-number of drops?
Your 20ml of methylene blue should last about 80+ tests, right?
el aguila
Member
That is kind of a loaded question.
Depends on several variables - type of carbon used, amount, and what is in your water.
For instance, the Rox absorbs and reaches it's full capacity much quicker therefore needs to be changed more often.
Ken Feldman (Penn State chemist) did a presentation at our club. Rox and the cheaper carbons absorb close to the same amount. The cheaper just takes twice as long to absorb the same amount as the Rox.
On my 400G total volume, I run two carbon reactors splitting the normal amount of BRS liginite between the two and change them out on alternating months. This way I'm not shocking my system by cleaning the water when changing carbon out. It also gives me some flex in the event that the tank gets over fed, I can add more carbon to each reactor and change them out more frequently.
Depends on several variables - type of carbon used, amount, and what is in your water.
For instance, the Rox absorbs and reaches it's full capacity much quicker therefore needs to be changed more often.
Ken Feldman (Penn State chemist) did a presentation at our club. Rox and the cheaper carbons absorb close to the same amount. The cheaper just takes twice as long to absorb the same amount as the Rox.
On my 400G total volume, I run two carbon reactors splitting the normal amount of BRS liginite between the two and change them out on alternating months. This way I'm not shocking my system by cleaning the water when changing carbon out. It also gives me some flex in the event that the tank gets over fed, I can add more carbon to each reactor and change them out more frequently.
el aguila
Member
I might add that Ken Feldman has some good articles out there. Both of these below are the Part 1 of 2 part series. I'ld highly recommend reading these and other similar articles.
http://www.advancedaquarist.com/2008/8/aafeature3/
http://www.advancedaquarist.com/2008/1/aafeature1
http://www.advancedaquarist.com/2008/8/aafeature3/
http://www.advancedaquarist.com/2008/1/aafeature1
The carbon is in a DIY up flow PVC reactor. I plan to open the reactor and scoop out a sample for testing. In doing this, I am assuming the bed is mixed well. I can't see inside the reactor to determine whether the bed is tumbling and mixing. I test 1/2 teasspoon which is about 1 gram of dry GAC. Twenty drops is about 1 ml, so, if I were to use 5 drops per test (I will likely use less), that works out to 80 tests. Powdered methylene blue is also available which would be cheaper yet. Salifert sells a test kit for activated carbon, but I figured that I would have some fun creating the test from scratch.
I just read a thesis that showed the correlation between iodine adsorption and dissolved organic compound adsorption. I am more confident now that methylene blue adsorption is at least roughly indicative of carbon exhaustion.
Thank you.
Interesting. It would be nice to know when its really time to change it out. All I've ever read about carbon is, mixed opinions on when it's exhausted. Some say 24hrs and some say up to a week. When my skimmer is getting close to needing a good scrubbing of the pump. I can tell (at least I "think" I can) when the fresh carbon is done doing any major work. The skimmer will slow down and not do much until the carbon gets loaded and then the skimmer starts to kick it in gear. I've had this happen as fast as 48hrs and then it's taken a week before. Just depends on how often I run the carbon. I also don't run the recommended amount (I'm currently using Sea Chem Matrix) for my tank size. I run about a 1/3 of the recommended amount in a bag.
Depending how much dissolved organic material is accumulating in the aquarium will determine whether you change the carbon every two days or after twenty days. As you are aware, we can't measure DOM. Methylene blue or iodine adsorption can give you an indirect answer to the level of exhaustion of the GAC. There are really no reliable rules of thumb to estimate amount or frequency of change.
If all the science and logic are ruining the hobby experience for you, follow the instructions on the jar of GAC.
mixedreeftank
Member
I let my ride for a month.
I am still refining the methylene blue test, but it seems the capacity of my GAC is showing signs of declining capacity after six days. Not exhausted by any means, just less capacity than when fresh. I may end up switching it out after two weeks, but time and testing will tell.
Charlene
Certified Reef Fanatic
Here is a neat video on how to know when to change carbon using only a couple of white buckets
https://www.youtube.com/watch?v=to3w0XN4kvY#t=24
https://www.youtube.com/watch?v=to3w0XN4kvY#t=24
ClownBubbaJoe
Member
How much of our additives like strontium, iodine, moly, etc, will be absorbed by leaving the carbon in for several days to 30 ?
I don't have any idea whether my method of using carbon and trace elements is correct or not, but I only use carbon for one week per month. I turn off the skimmer, remove the carbon and other media, then add my additives. After 3 days, all is turned back on and new media added.
Do you agree or am I too anal about carbon absorbment ?
I don't have any idea whether my method of using carbon and trace elements is correct or not, but I only use carbon for one week per month. I turn off the skimmer, remove the carbon and other media, then add my additives. After 3 days, all is turned back on and new media added.
Do you agree or am I too anal about carbon absorbment ?
Reef Frog
New member
Here's a low tech method. During a water change, put equal amounts of your tank water and newly mixed salt water in seperate white buckets. If the tank water has a noticeable yellow color, you're seeing disolved organics which may indicate your carbon is exhausted. You can then "prove" that to yourself by doing the same test again in a few days after a GAC change and see if the water has cleared up and you'll know the GAC absorbed the material. However if you have lots of unicellular algae in the water column that may interfere with the results.
FraggledRock
New member
in that case, whenever you want! lol =P
You have the option of completely exhausting the GAC, or taking it out before it becomes less effective.
I would say monthly is about right though. also the amount in there changes the variable...
either way I cant see it being that big a deal.
FraggledRock
New member
would 4x that work on a monthly routine?
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