#2: How does an activated-carbon water-filter work?

This $43 4-stage water-filter reduces TDS to 110 (instead of 0-20 that is normal in a 5-stage water-filter).
The carbon filter is effective to remove copper, that can kill shrimps.

110 TDS maybe ideal, as the ideal TDS range is 150 to 250 for cherry and crystal, or 100 to 180 for Taiwan bee, requiring no further remineralisation to achieve the target TDS.
However, for non-cherry shrimp, a shrimp sand is still required to further reduce pH to 6 to 6.5.