I am talking about liquid carbons that aid in plant photosynthesis and growth. Products like Excel, API CO2 Booster, and Metricide 14. These are good products to use daily in planted tanks BUT several plants are known to be sensitive to it, like Riccia.
Activated carbon in planted tanks is a very debatable subject which you will get arguments on both sides of the fence. I personally use carbon in my planted tanks and have never had issues with plants. Many prefer to use Purigen in planted tanks.