What is the difference between liquid aquarium plant fertilizers and root tabs, and when should I use each?
Liquid fertilizers add nutrients to the water, so they are ideal for plants that take in most nutrition from the water column and for mixed planted tanks. Root tabs put nutrients directly into the substrate, which helps heavy root feeders that draw most nutrients through their roots. Many aquariums use both to cover water-column needs and root-zone feeding at the same time.
Do aquarium plants need a CO2 supplement in addition to fertilizer?
Not always. Fertilizer provides essential nutrients, but plant growth also depends on light and available carbon. Low to moderate light or beginner setups often do well with fertilizer alone, but high light or densely planted tanks may benefit from adding a CO2 supplement and using a simple indicator to keep levels in check.