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Permalink Reply by ŦůRbö ۰ Ҏяѻ ۰ on December 10, 2012 at 4:20pm

Carbon will remove potassium and other trace and minor elements if they are in a specific form, which is pH dependent. For most elements, the pH must either be below 4 or above 10 for them to be in a chemical form that can be absorbed by carbon. Under most conditions, carbon has a functional life of one to two weeks, perhaps even shorter. The average functional life of carbon is difficult to determine as many variables apply, such as the amount of dissolve organics in the water, the effectiveness of mechanical filtration, and the amount of carbon in use.

A safe assumption is that carbon’s functional life in most tanks will not exceed 2 weeks. With this assumption, a best practice is to replace half of your carbon weekly. This will result in fresh carbon within the tank for each week with no carbon remaining in the tank for longer than two weeks.

All carbons will release some amount of phosphate but some inexpensive carbons are acid washed in phosphoric acid and these carbons will leach a substantial amount of phosphate into the water (which promotes algae growth). However, all carbons from reputable manufacturers are currently acid washed with hydrochloric or sulfuric acids. These will leach very little, if any phosphate. Provided you are not a reef aquarist (and since this Post is about carbon use in a freshwater tank that is unlikely) the amount of phosphate leached is irrelevant.

Regardless, phosphate concerns can be eliminated by soaking activated carbon in a saltwater solution for a few days prior to adding it to your aquarium. Carbon can mask problems. As an example, a dead rotting fish in a tank will normally cause the odor of the water to change. In the absence of carbon this odor may be detected by the aquarist who may then search out the cause, find the dead fish, and remove it from the tank. If carbon is in use, the odor of the water may not change, and the dead fish may be left to decay potentially resulting in problems far more significant than a smelly tank.

I prefer not to use it in a planted tank; it will remove most of liquid fertilizers. The main reason people use it is to remove smell and the chemicals they add to city tap water. But with weekly water changes there will be no smell, and the use of a quality water conditioner will remove chlorine and other chemicals in the tap water.  

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Permalink Reply by viper15a on December 10, 2012 at 8:14pm

I just want to say that was a great reply, Turbo! Thumbs up, bro

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Permalink Reply by Robert Jango on December 13, 2012 at 1:47am

In the early days of the hobby carbon was an all-purpose substance for making tap water safe because municipal water systems were not as reliable as they are today. These days nobody really uses it because our tap water is not only safe but actually beneficial for fish once you've removed the chloramine. Also, as Turbo says carbon binds with lots of minerals that plants need to grow; so there's another big reason not to use it.

In places with acid rain (not to be confused with rainwater that's acidic) carbon helps remove the pollution that comes from coal refineries. One of these areas is along the Wyoming/Montana border and another is Lexington KY (Dustin's neighborhood). This is kind of sad because rainwater works like magic on some of the cichlids Dustin brought back from Peru. I remember a video he made awhile ago about how he was planning on collecting rainwater from his roof. Not sure why he didn't follow up on this idea but the coal refineries next door might be the reason.

Supposedly regulations requiring [coal scrubbers?] cut out the pollution from these plants but I'm not sure if this is true or not. 

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