Healthy plant growth depends on CO2 amount, lighting, and nutrients in the aquarium. There are two types of nutrients essential for plants: macronutrients (nitrogen, phosphorus, and potassium) and micronutrients (trace elements such as zinc, boron, iron). Nutrient deficiency in plants can be easily observed;slow plant growth and yellow leaves indicate nutrient supplement is necessary. The fertilizer should contain elements from both macro and micronutrients.
Nitrogen, phosphorus, and potassium are key macronutrients. Plants need these minerals in larger amounts. Some of these macronutrients are available in the aquarium water, fish food, and fish waste.
High nitrogen levels in the water can harm the fish population in the aquarium. Usually, aquarium water consists of three different forms of nitrogen—ammonia, nitrite, and nitrate. Ammonia from fish waste can be converted to nitrite and nitrate by beneficial bacteria in the aquarium. Plants help to reduce the nitrogen level in the water because they have the ability to use the different nitrogen forms in the aquarium water and if the tank is full with plants, the nitrogen level can decrease very quickly.
The appropriate nitrite level is 0.2mg/ml and nitrate level is 25ppm. Nitrite and nitrate levels should be controlled regularly. If there is a lack of nitrate, nitrate addition is recommended. Also, in case of the excessive amount of nitrate, the aquarium water should be partially changed.
Phosphorus is an important element for plant health. Plants need additional phosphorus in high light.Yellow leaves are signs of phosphorus deficiency. Plants are able to get enough phosphorus from available sources;therefore, it is not necessary to add phosphorus in the tank frequently because fish food and fish waste contain phosphorus and plants can use the mineral from these sources. Excessive phosphorus can cause algae problems and can be harmful for the fish, thus check the levels before adding any to the tank.
Potassium is necessary for healthy and strong plant growth. Plants need potassium additives because the fish food and waste doesn’t supply enough potassium. Potassium is found in commercial aquarium plant additives that can be purchased as a supplement for plant growth.
There are ten main trace elements essential for plants usually found in the aquarium water. When plant growth is fast,plants need to use high amounts of micro elements in the water. It will be necessary to purchase a fertilizer for plant that contains iron, manganese, boron, zinc, magnesium sulphur, and cooper. It is also possible to prepare fertilizer at home, though due to the preparation it is not recommended.
Types of Fertilizers
Substrate fertilizers can be in powder form containing laterite, which should be mixed with a deep layer of the gravel to provide iron to the roots of the plants. Laterite must be lightly applied on the lower layer. The substrate should be thoroughly mixed with the lower layer; otherwise laterite can increase the iron level in the water and cause algae problems.Combined fertilizer packages can be purchased for plant aquariums.
Besides the powder form, substrates are available in tablet and stick form or plant spike fertilizers usually used for houseplants. However, some of these can be toxic for aquarium plants due to the high amount of urea and nitrogen level and low level of phosphorus, which is preferred for aquarium plant growth. These spikes should be placed in the substrate to allow only the plant roots to absorb it.These types of substrate fertilizers minimize algae because algae cannot reach the nutrients in the substrates.
Liquid fertilizers are good for aquarium plants since some plants do not have roots. This fertilizer will supply all the necessary nutrients because they mainly contain micronutrients and are suitable for daily or weekly dosing. Excessive usage of macro-elements is not recommended due to problems with algae. Partial water replacement is recommended in order to prevent accumulation of the fertilizer in the tank.
Nutrients contribute to the plant growth in the tank; however, if the plant condition is not changing, excessive usage of the fertilizer is not recommended. Hobbyists should be sure plants receive enough light and if the room environment is unsuitable for plant growth the tank should be repositioned.