Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Look at the active ingredients in each product.
Plants use over a dozen different elements to grow.
Some are already supplied, so we do not have to add them.
Others should be supplied to keep the plants growing well.
Most tablets for the substrate are slow release, so whatever they provide is provided in small amounts over a long time. This is good, you do not have to dose (add tablets) very often.
Most water column products are short lived. They get used by the plants or microorganisms in the tank pretty fast, and some types of substrate can remove them from the water. Water column dosing needs to be done more frequently.
Here is the tricky part:
Fertilizers in the tablets can find their way into the water column. If you are also adding some of the same fertilizer via daily dosing that might become an over dose.