Some points to consider.
1) Cost. Dosage, how much pills to use for a 5ft tank with sump? Will it be practical to use them for fish tanks? Why not use activated carbon bags found in most LFS?
2) A good mechanical filter is needed. After breaking down into powder and adsorpbing all the pollutants, you'll need a good mechanical filter to separate the powdered carbon (loaded with pollutants) from the water. If not removed from water, the carbon powder will continue adsorbing pollutants until its maximum capacity... and then... release the pollutants back into water again. Just like the activated carbon bags used in filters. You need to change them regularly.
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