A well landscaped aquarium can be as delightful as a well-planned garden. A miniature ecosystem, it has the advantage of including colorful fish as well. For flourishing growth, you need to make sure that nutrients are available to the plants in the right quantities, as an over supply can be toxic to your vegetation as well as the fish.
Fertilizer is composed of one or more elements plants need to grow properly. Some elements needed, such as carbon and oxygen are supplied naturally by the dissolved air in the water. Nitrogen, often included in fertilizers for non-aquatic plants, is produced by the fish as waste, so you need less of this in a planted tank. Some minerals, such as iron, copper, zinc and calcium are needed in extremely small quantities and adding too much can be harmful.
Adding fertilizer to your aquarium can boost plant growth but, because it is a closed system, nutrients can build up to toxic levels over time. Many aquarium enthusiasts combine fertilization with frequent water changes to avoid this problem.
Aquatic plants can absorb nutrients through both their leaves and roots, so the type of substrate, soil or gravel mixture, you plant them in will influence the need for fertilizer. Some mixtures include soil or nutrient-rich components, some simply anchor the roots without supplying food for the plant.
The type of plants you grow will influence the amount of fertilizer you need to add. Some are heavy feeders, some need little supplementation.
You'll find fertilizers sold in three different forms. Solid fertilizers are placed in the root zone, in the substrate, and are absorbed mainly by the roots. These are best added when you set up the aquarium.
Liquid fertilizers permeate the water and will be taken up by the leaves. Excess amounts are easily removed by simply changing the water.
You drop tablets into the aquarium and they dissolve into the water. The amount used depends on the volume of the aquarium and, like liquid fertilizers, can be removed by changing the water.
Symptoms of Deficiencies and Excess
Keeping an eye on your plants will help you catch deficiencies or symptoms of excess nutrients quickly. Yellow leaves can mean a lack of nitrogen, iron or sulfur. Yellow spots on the leaves can indicate too much iron or a deficiency of potassium or phosphorous. Small spots of green algae on the grass mean the tank needs phosphate. A potassium deficiency can cause small holes in the leaves.
Use only fertilizers formulated for aquarium plants, not general-purpose garden fertilizer. Their nutrients are not adjusted to the needs of aquatic plants and they may poison fish.
Change a portion of your water frequently, weekly or every other week, to prevent the buildup of nutrients and waste products to a toxic level. Repeated water changes benefit both your fish and your plants.