Guide to Growing Freshwater Aquarium Plants

Have you ever seen a well planted aquarium? The first time I saw one was when I walked into an aquarium pet store and saw this huge 300 gallon display aquarium built into the wall and containing the most incredible display of plants and wood I had ever seen. Watching it was hypnotic. Everything looked so natural and real. It was as if I was standing before a window into another world.

Then I began reading about the Japanese planted aquariums made famous by Amano and traditional Dutch planted aquariums. I saw people were using plants in the aquarium as they would in creating an outdoor garden. Every time I tried to grow plants they would just wither away. So what are these peoples secrets?

Well it’s no secret. Just science. There are some basic elements needed by plants in order to grow. Once you figure out how to provide those elements, the rest is pretty easy. The basic elements are light, nutrients, and C02.

 

Light

All plants need light in order to grow. Light gives the plants energy and is part of the process of photosynthesis that turns the energy into fuel. The intensity of the light is the most critical aspect. The most common problem hobbyists face is the light fixture that came with their aquarium is not capable of providing intensive enough light to grow plants regardless of the brand of the bulb used.

The easiest way to gauge how much light you need is to use the watts per gallon rule. While it may not be 100% accurate, it is the most simple way to give an estimated guess. Based on the average brightness of a standard fluorescent bulb, 2 to 3 watts of fluorescent light per gallon of water is considered ideal. Obviously if you have a 30 gallon aquarium and it came with a single 15 watt fixture, it is not enough light. You then have the choice of either adding additional strip light fixtures to equal 60 to 90 watts total, or replace the 15 watt fixture with one that provides higher wattage type fluorescents such as T5s.

 

Nutrients

There are two types of nutrients plants need to grow. What’s called Macro nutrients, which plants use in the largest amounts:
NO3 = nitrate
PO4 = phosphate
K = potassium
Ca = calcium
Mg = magnesium

Micronutrients are minerals that are just as important but used to a much smaller degree. Iron for example is an important mineral for photosynthesis. Nitrogen in the form of either nitrate or ammonium is provided to plants by fish waste. A well established aquarium may have a fair amount of this accumulated under the gravel. Phosphate may be contained in tap water and is a part of many fish foods. Calcium and magnesium is also in tap water except for very soft water. Potassium may be in tap water to some extent but is often added to the water or substrate in the form of a fertilizer. Trace minerals such as iron may be in your tap water as well but are difficult if not impossible to measure. These are usually introduced as a fertilizer.

 

Fertilizer Delivery

Fertilizers are either introduced via the substrate, (gravel bed) or to the water. Most plants readily absorb nutrients either from their roots or through their leaves. They will take whichever is more readily available. The commercial substrates you see advertised for plants are usually some form of clay gravel that provides iron and other minerals. It may or may not be fortified/processed to include some macronutrients. Fertilizer tablets for the aquarium are available that provide Macros, minor nutrients, or in some cases a combination of both. Liquid fertilizers are usually either micronutrients or a combination of micros and macros minus the nitrogen, (nitrate). Aquariums with high intensity lighting require more fertilizer more often while aquariums with low to moderate lighting require less nutrients less often. Frequent water changes can prevent excess levels of unused nutrients building up.

 

C02

Carbon dioxide is an essential element of plant physiology. Without it plants cannot properly go through photosynthesis and grow. True submersed aquatic plants have evolved to find traces of C02 from bacteria, but most of the plants we have in the aquarium actually grow above water to obtain C02 and in order to thrive they way we would like them to underwater C02 must be introduced . For most aquarium plants the ideal C02 level is anywhere from 10 to 25ppm. C02 is added to the water by either a pressurized gas system or a fermentation system that uses yeast and sugar to create the gas that is then fed into the aquarium. Pressurized gas gives you complete control over the amount of gas going in the water, while fermentation systems have no control and produce enough gas to meet the minimal requirement. Low tech plant tanks rely on slow growing plants under moderate or lower light levels obtaining small amounts of C02 from decaying organics and bacteria in the substrate, often provided by the use of soil underneath the gravel.