03-25-2010, 12:06 PM
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First on what plants do need: 17 nutrients, of which 13 are mineral. Some of these will occur from fish food and fish waste and organics breaking down via bacteria in the substrate. Carbon (as CO2) and nitrogen (as ammonia/ammonium) come from the fish and biological actions in the aquarium. Others might be present in your tap water and will be replenished during the weekly partial water change; I'm thinking mainly calcium and magnesium here, these are the minerals that determine the hardness of water so the degree of hardness of your tap water will indicate if these are present.
Without knowing all the above, it is difficult to say whether you will or will not definitely need a good liquid fertilizer. Most of us find we do need it, but it varies depending upon all those things and from aquarium to aquarium. Plant the aquarium and observe the plants; they will show signs of nutrient deficiency if something is lacking, and if you are at that point able to buy a good fertilizer, they will recover.
As for the fertilizers themselves, not all are good. Root tabs work well with substrate rooted plants, and less so with stem plants. For plants that root on wood and rock (like Anubias, Java Fern, Java Moss) or floating plants, substrate fertilizer will be useless.
Liquid fertilizers are the best overall, as all plants can use them. Nutrients come from the water, assimilated via the plant roots and in some the leaves as well. The liquid has to be a comprehensive one providing most of what the plants need that is likely to be missing from the water, fish food, etc. I mentioned above. Seachem's Flourish Comprehensive is good, I use it. I do not recommend the API Leaf Zone nor the Tetra because they are not complete. There are some others, if you can tell me what is available at your stores I can comment.