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Mastering Freshwater Aquarium Ecosystems

Table of Contents

  1. COVER
  14. ROCKS
  15. WOOD
  16. PLANTS


There is nothing quite like an aquarium with live plants living in harmony with the fish. The benefits of live plants in the aquarium are numerous, they provide hiding places for fish fry, material to build nests, places to hide from aggressive fish, and they help reduce algae growth. Not all fish are suited for planted aquariums. Many fish will eat plants and dig up their roots. Many of the gouramis, livebearers, killifish, tetras, barbs, soft water dwarf cichlids, angelfish, discus, and small catfish are excellent choices for the planted aquarium.

Aquarium plants play a major role in keeping nitrate accumulation in the ecosystem under control. Without plants, nitrate will accumulate quickly, and necessitate larger and more frequent water changes.

There is a general rule you should remember when buying plants, "If it looks like a houseplant, it probably is." Many pet shops sell plants targeted to the aquarium hobbyist that are bog plants. These bog plants will start to decay after a few weeks being planted in the aquarium. Make sure the plants you choose are true aquatic plants. Plants that cannot support themselves out of the water are usually good choices for the planted aquarium. Avoid plants with rigid stalks and leaves. There are exceptions to these rules, like Anubias barteri and Anubias nana, but in general they are good rules to follow.

If you have fish that like to dig in the substrate, there are some choices of plants that float at the surface. Water sprite (Ceratopteris pteridoides and Ceratopteris thalictroides), crystalwort (Riccia fluitans), duckweed (Lemna minor), and water lettuce (Pistis stratiotes) are all examples of floating plants that can be used in an aquarium where rooted plants would not be possible. Keep in mind though, floating water plants limit the amount of surface area that is in contact with air. Increasing water flow can help offset the amount of gas exchange lost to floating plants.

In cases where the fish you are trying to keep eat plants, you can connect a hydroponic system or refugium to the aquarium to remove nutrients. Plants that grow in a hydroponic system are generally more efficient at removing nutrients than submerged aquatic plants in the aquarium, as they are exposed to carbon dioxide rich air, and the light is not filtered out by the water. The other option is to use a refugium for filtration that can also be used to house small fish or shrimp.

The type of plants you select for the aquarium will directly affect the rate of nutrient uptake. Fast growing plants will typically be the best choice for aiding in nitrate reduction. Fast growing plants will also use CO2 more quickly therefore you will need to have a good water flow to increase the amount of CO2 that will be introduced to the water column.

The depth (height) of the tank should be considered when selecting plants, as some will not do well in deep aquariums. Some species of plants likeVallisneria gigantia can grow leaves over 6 ½ feet (2 m) long. In shallow aquarium, Vallisneria gigantia leaves would quickly grow to the surface and block out light.


Laterite is clay soil rich in iron, and is usually a red color. Most plants need iron to thrive in an aquarium. Laterite can provide long term constant source of iron to rooted plants. Sand substrate is the best when laterite is used, as it will help keep it under the bed.

This planted aquarium has laterite in the bottom half of the substrate to provide iron to the roots of the plants.

Laterite is typically added to the bottom half of the aquarium substrate. First wash out the substrate for the aquarium, then mix one half of the substrate with laterite. Lay this laterite rich substrate on the bottom of the aquarium and then cover it up with clean substrate. After all the substrate has been added to the aquarium, lay a plate on the substrate, and pour the water into the aquarium on top of the plate, taking care to not to disturb the substrate. The aquarium will be a little cloudy for a few days until the fine sediment is filtered out or settles to the bottom.

If your aquarium is already set up, there is an alternate plan you can take to add the laterite to the gravel. First mix the laterite with a little bit of water until it is muddy. Draw the watered down laterite into a large syringe or turkey baster and inject the mix into the lower level of the bed.

The disadvantage of using laterite is when you pull plants out of the bed, you will usually bring some laterite to the surface. For aesthetic reasons, this is undesirable.

Aquatic plant fertilizers are formulated differently than terrestrial plant fertilizers. Plants in the aquarium often have ammonium, nitrate, and phosphate in abundance from fish waste, so typically you do not want much of these elements in the aquarium fertilizer, otherwise you will likely have a very heavy algae bloom. Plants require major and minor trace elements to grow and reproduce. Trace elements and/or light are the limiting factor in plant health. Plant growth can be stunted when any one element that it needs is in short supply. Different species of plants require different levels of trace elements to thrive. In some cases, some plants in the aquarium will seem to do just fine, while others will struggle. In some cases, just the addition of a liquid iron into the aquarium system will make all the difference in plant growth.

A good all purpose aquatic plant fertilizer will have higher values (major trace elements) of iron (Fe), potash (K2O), magnesium (Mg), sulfur (S), sodium (Na) and calcium (Ca). There are many minor trace elements, of which nitrogen and phosphate should be only in very minor amounts.

Injecting Sand Bed with Aquatic Plant Fertilizer
Injecting the sand bed with aquatic plant fertilizer. This technique delivers the fertilizer to roots, and away from algae.

Liquid plant fertilizers are normally added to the water column. My preference is to inject it into the sand bed with a plastic syringe. The fertilizer is mixed with about 20 parts aquarium water, drawn into the syringe, then a small amount is injected every two inches (5 cm) into the bed. This helps keep most of the nutrients in the bed, and away from algae.

The frequency and amount of fertilizer added to the aquarium will depend on the plant load, species of plants, and lighting. Every aquarium ecosystem need for fertilizer will be different. The instructions on a fertilizers bottle is only a general guideline, you will most likely need to adjust the quantity and frequency based upon how plants or algae react to your dosing.

Root tabs are another form of fertilizer that can be pushed into the substrate near the roots of plants. Root tabs are very effective for growing Amazon sword (Echinodorus bleheri) plants. The only drawback is when you pull plants up from the bed the fertilizer gets released into the water column, sometimes resulting in an algae bloom.

Baking soda (sodium bicarbonate) will raise the pH/alkalinity of the aquarium, and it will also provide a source of carbon for many species of plants. Vallisneria species of plants will often respond quite well to ½ to 1 teaspoon of baking soda added per 10 gallons (38 l) of water. The increased alkalinity of the added baking soda will also help maintain a more stable pH.

Calcium and magnesium can be added to the aquarium to increase hardness. Many species of plants will do better if the calcium and magnesium levels are elevated.

Potting Soil
Potting Soil Planted Aquarium
This aquarium is set up with potting soil in the bottom to grow Italian Val (Vallisneria spiralis).

Potting soil under the sand bed is a technique that works quite well in providing plants long term nutrients at the roots. While the tank is empty, potting soil at about 2 inches (5 cm) in depth is placed on the bottom of the aquarium. Substrate at about 1 ½ inches (4 cm) is placed on top of the potting soil. A plate is placed on top of the substrate and water is then poured into the aquarium slowly so the bed does not get disturbed.

Potting soil technique is a great way to grow and propagate plants quickly to be used in other display aquariums. The drawback of the potting soil technique is when you pull plants out of the bed, potting soil will be brought to the surface of the substrate. While this does not cause any adverse effect to the system, it does look unsightly.

Another alternative to adding potting soil on the entire bottom of the aquarium, is to add it to pots or other containers. This way you can pull the container out of the aquarium before removing plants and then re-pot.

Cyanobacteria (Slim Algae, Blue-Green Algae)
Freshwater Cyanobacteria
There is a simple remedy for eradicating cyanobacteria from the aquarium, the addition of erythromycin to the water and treat every other day for six days is normally all that needs to be done. Make sure there is no activated carbon in the aquarium system when treating with erythromycin.

Cyanobacteria often shows up in newly set up planted aquariums. It is typically a dark green in color, and can be removed from surface area in sheets. Cyanobacteria are bacteria that obtain their energy through photosynthesis. Cyanobacteria can cover sand, rocks, glass, and plants in the aquarium. Excessive growth can cover plants to the point where they can block light to the plants.