[ellebelle]

Where is part 2?

[prattreef]

http://www.advancedaquarist.com/2008/2/aafeature1

[CraigBingman]

Quote: Originally Posted by House of Laughter There IS a difference between carbon types and we should read this article and understand the differences between them: http://www.advancedaquarist.com/2008/1/aafeature1 - part 2 is also available, but way more technical. Bituminous coal covers reef keeping needs more broadly then lignite due to it's binding capabilities.

It is a nice piece of work, but I think it falls somewhat short of the threshold where we can pronounce that GAC derived from bituminous coal works better that GAC from lignite coal for aquarium purposes. What was demonstrated fairly convincingly is that the BitGAC did a better job of binding small dye molecules than LigGAC.

Unanswered questions:

Does BitGAC perform better or as well as LigGAC for binding larger molecules that might also be quite relevant to aquarium husbandry?

We might specifically ask how well the two types of carbon decolorize aquarium water with some sort of steady state population of humic/fulvic acids that accumulate in the water over time? These molecules can be substantially larger than the small dyes (all under 1000 atomic mass units) included in the study. These compounds are quite heterogeneous, but usually fulvic acids are somewhere between 1000-10,000 amu, and humates are 10,000-100,000 amu.

Marine "Gelbstoff" (naturally occuring blue-fluorescent yellow compounds in seawater) are thought to originate by the oxidation and cross-linking of unsaturated fatty acids. There have been a number of studies on these compounds, and it is generally known that bits and pieces of both the marine and terrestrial humates are similar. Of the dyes that they studied, fluorescein looks the most similar, but it seems too small to be a really good model.

In any event, I'm unconvinced that the small molecule dyes used in this study are necessarily reasonable proxies for marine gelbstoff or other specific classes of compounds of concern, such as allelopathic compounds screted into the environment, or compounds related to iron sequestration.

Activated carbon can also do a number of things in a marine tank, that are unrelated to the prompt ability of the carbon to decolorize water. It is fairly well established that old carbon in low flow areas develops internal anoxic regions and participates in denitrification. To do that, it needs enough pore spaces large enough to support bacterial growth. Of course, bacteria are immensely larger than any of the dyes used in this study.

So if you have a hankering to dump some small molecule dyes into your tank, this article pretty conclusively shows what kind of carbon would best remove it. But the question of what carbon is best for aquarium husbandry is still open in my mind.

[CraigBingman]

Quote: Originally Posted by House of Laughter;463785 There IS a difference between carbon types and we should read this article and understand the differences between them: [URL http://www.advancedaquarist.com/2008/1/aafeature1[/url] - part 2 is also available, but way more technical.

I'll do this again, since the first reply apparently went into the bit bin.

Part 1 and 2 of the above article are very nice work, but they fall short of settling which kind of carbon is actually best for reef aquarium use.

The main problem is that all of the surrogate molecules used in the study are quite small, much smaller than the average molecular weight of either yellowing compounds in seawater, or specific allelopathic compounds secreted by various organisms to gain competitive advantage. Fulvic and humic acids range from 1000 atomic mass units (amu) to over 100,000 amu. All of the surrogate compounds used in the study are under 1000 amu. Of the compounds picked, probably fluorescein is the closest match chemically to marine gelbstoff (still too small, though, and probably higher aromatic/aliphatic ratio than material that is formed by autooxidation and polymerization of polyunsaturated fatty acids.)

Activated carbon can have other roles in reef systems beyond its ability to promptly remove low molecular weight dye molecules. Old carbon gets colonized by bacteria, and in low flow environments, probably participates in denitrification. The last time I saw Peter Wilkins, he shared with some excitement with me the research of a young German scientist who looked into this.

Although it is somewhat inconvenient to work with the "real thing" (the actual compounds found in marine tank water) it certainly has been done. For example, the first article that I wrote for Aquarium Frontiers studied the optical effects of removing real gelbstoff from a reef aquarium.

[House of Laughter]

Criag,

Great meeting you in Atlanta - AND for the cypher and decipher - but what does that mean exactly? can you give us some examples or perhaps a link to the article you wrote on what other benefits it provides - most general reefers here on MR see water clarity and removal of certain harsh toxins as the benefit.

Any additional insight you could provide is appreciated

House

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