Carbon and Salts

[Glenstorm]

Here's a quickie:

I know that carbon (in the filter)removes meds and some ferts from aquariums. Does it affect the salts we add to our cichlid tanks?

[RTR]

No, not to any detectable degree.

[predatorcichlid]

Once salt is mixed fully with the water there is no easy way to seperate it. Carbon will absorb any thing that can attach to the carbon chemically. It can also remove some trace elements and other things you might want in your water as well as bad. The bigger problem with carbon is it will also leach toxins back into the water column once it is used up and it is impossible to tell when the carbon has been spent. It could be a few hours to a week tops. Depending on what it has absorbed it could release worse toxins back into the aquarium than it took out. This is the main reason you don't seen many people use it.

[rus]

Originally posted by predatorcichlid
O The bigger problem with carbon is it will also leach toxins back into the water column once it is used up and it is impossible to tell when the carbon has been spent. It could be a few hours to a week tops. Depending on what it has absorbed it could release worse toxins back into the aquarium than it took out. This is the main reason you don't seen many people use it.
could you please provide proof of this statement. i have look for any data on this but everything that i have found states that carbon does not leach what it has absorbed back into the water.

[RTR]

There is no proof of that statement because it is a myth. Common as dirt on the boards, with no basis in fact at all that I can see. Folks just do not understand adsorbtion. The general idea apparently is that carbon is some sort of absorbing sponge and if you let it sit, or manipulate it wrong, the material will be squeezed back out - which cannot in reality happen under aquarium conditions. That is right up there with typing pl*co for pleco.

Frustrating. :mad:

[rus]

thank you that was my genaral thought on the subject

[predatorcichlid]

With out going into a chemistry lession activated carbon absorbs certain things by creating a chemical chain for them to cling to. Depending on what the carbon has taken in or how much this chain can be broken, thus re-releasing it back into the water system. Active carbon has a life span. Also combinations of chemicals found in aquarium water can combine to form a new substance this too can break free from the carbon cna cause problems in a aquarium.
Try this take the carbon out of your tank once it has been in there for a month. Place in clean cup of water. In a short time the water will discolor and smell. IF nothing could escape the carbon then this would not happen.

[mogurnda]

I don't feel strongly either way, but adsorption is a two-way process, like every other chemical reaction. Depends on the rate of the reverse reaction as to whether there is an issue here or not. If binding sites become saturated, then the on rate goes to around zero, and there could very well be leaching, depending on the off rate. Seems like there's a lack of experimental evidence on both sides of this discussion so far.

Not sure where the "hours to weeks" numbers come from. I don't use it in the freshwater tanks, but it is very commonly used in reefs. The general advice is to change it every few months to maintain effectiveness.

[scott]

I am by no means an expert but I would like to note the difference that some people are typing absorb and some adsorb. Adsorb is the correct term when talking about carbon.

[predatorcichlid]

For info on carbon Here are two books.
Marine Reef Aqarium Hand book by Dr. Robert Goldstein. This Book explains in detail the same thing I said. IT also states that carbon will remove trace elements and can leach everything it's removes back into the water sysem. From this point the reading get little thick.

The book, Water chemistry and filtration for your freshwater aquarium. States that carbon should only be used to remove medication or for 1 to 2 hours after a water change and should not be used as a regular method of filtration due to the fact it can release harmful waste products back into the tank. And then goes on the explain how.

I have a wall full of books, 1000+ gallons of water, and 16 years of experience. There not many people that know more about this hobby then me. If I give out info you can bet I can back it up. If you like I can look around. I am 100% sure I can find alot more about the subject if you like some deep reading. So much for the myth idea.

[RTR]

Just FYI, I have over 40 years in this hobby, advanced degrees in biochemistry and physiology, and ran pharmaceutical research and devlopment labs for decades. You are working with incorrect information.

Take your biomedium out of the tank and store it a cup of water as you did with the carbon and you will get the same result. It is the biofilm on the carbon dying and fouling the small sample, just as would your biofilter. That tests nothing about adsorbtion release.

[mogurnda]

There not many people that know more about this hobby then me. Golly, I guess that little old me sitting in a roomful of biochemists should just keep quiet.

Seriously, though, many of us are also very experienced, have walls full of books and may have opinions that differ from yours. Sprung and Delbeek present a different view of carbon than you do. Does that mean that they are wrong? I find well-considered arguments and evidence much more convincing than statements like the above.

I think the point RTR was making was that many popular books state things without much in the way of experimental evidence. They make convincing arguments, but without data, they are simply that. So here's something that would be certain to shut people up: do either Goldstein or the water chemistry book cite actual data to support their proposition? If not, then the issue continues to dangle.

RTR, I have a question for you. Are you saying that adsorption to carbon is irreversible? As a biochemist, you know that adsorption is usually reversible (or chromatography would be a waste of time), so how do we know that stuff stays permanently stuck to activated carbon?

[RTR]

You can get it back off with strong alkalis - way up there >>pH 10.5. Of course any fish or plants present in the same solution will already be toast before the adsorbed material releases. It is a comparable situation to iodized or other additive-treated salt - before you could get to toxic levels you would have pickled any biologic critters present with the NaCl itself. Yes you can get adsorbed material off, but not under aquarium conditions.

I have heard there are other processes, but have not looked into them myself - there should be some.

Or you can dry it and run back through the activation ovens, with a reducing atmosphere and high temp, but then you have fine ash to deal with. And for the DIYers still reading: no, your self-cleaning oven cycle will not do the job - that is a an oxidizing atmosphere with moderately high temps.

[mogurnda]

Allright, I decided that the best idea would be to ask the lab chief here about the issue. He is a member of the National Academy of Sciences, and has been doing biochemistry since before most of us were born. And he refuses to offer opinions about things he doesn't know initmately.

The quick summary is that predatorcichlid is generally right about the mechanism and that it's reversible. The "carbon" is really a lump of heterogeneous compounds that allows a wide variety of molecules to bind. If it were pure carbon, it would only bind a narrow range of molecules. These bonds are not covalent, so they are reversible.

The effective life of carbon depends on the concentration of the substances that are being filtered, and the number of available binding sites, so I'll stick with my original opinion that it can be used longer than a few hours or days under normal circumstances.

The debate about carbon will probably outlive me, though, regardless of what I say.

Glenstorm:

The original question was about salts, though. Here is an opinion based on my own measurements. I use it on my nano reef, because the leather coral is well known to produce compounds that inhibit other corals. Of the ions I can test, like Ca and HCO3, and NO3 there is no measurable effect.