Hard-to-Grow Aquatic Plants

Here are some tips for growing difficult aquatic plants.

Q. I have an aquarium that was consistently giving me problems with disease and algae. I would treat the aquarium with chemicals, and everything would get better. As soon as I quit treating it, everything would get worse. While researching how to solve the problem, someone told me to put live plants in the aquarium. For the last year and a half, the aquarium has been free of diseases, algae blooms and chemicals. I have not lost any fish since I put in the aquatic plants. This has caused me to research live plants. I’m trying to find out what the aquarium setup is for plants that would be classified as hard to grow or requiring very bright light (i.e. substrate, aquarium size, lighting, etc.).
John Tompkins
Gaithersburg, Maryland

A. Someone could write a whole book on the different ways to set up planted aquariums. I’ll try to be briefer with some rules of thumb. Plenty of different methods work, though some people seem to have greater success with one or another method. Also, different “hard-to-grow” aquatic plants are difficult for different reasons. Some might be thought of as difficult because they require frequent pruning or replanting. Some grow and use the nutrients in the water quickly, and some need much more light than other aquatic plants.

The best way to handle the level of pruning is with the choice of plants and the amount of light provided. Nutrients are something easily controlled by dosing and water changes. There’s only one way to deal with high light requirements, and that means using ample amounts of it.

There probably is not any aquatic plant you will come across that cannot grow well with 2 to 3 watts per gallon (wpg) of power compact fluorescent lighting with a high-quality specular (mirror finish) reflector. All light bulbs (incandescent, fluorescent, high output florescent, metal halide, etc.) give off less light the longer that they are used. If you use them, they will dim. So if you are aiming for 2 wpg, you might actually install something rated higher, then just have to change the bulbs less often. Fluorescent bulbs dim more slowly the longer they are used. In the first few hundred hours, they will dim about 20 percent, but they will only dim about another 20 percent over the rest of their lives.

Aquariums size matters only in relation to the size of the aquatic plants you are growing. My smallest aquarium is about three-fourths of a gallon, and my largest is 150 gallons. The size is more important than the shape. Aquariums that are not very deep front-to-back are difficult to aquascape. Relatively tall aquariums will accept larger aquatic plants as far as height goes, but if they are not very front-to-back, large plants still will not fill well; so for example, a 30-gallon long is preferable to a 30-gallon high.

The standard 15 gallon has great proportions for a small planted aquarium. The standard 55-gallon aquarium is simply too narrow front-to-back. I think the standard 75-gallon aquarium is about perfect for a mid- to large-size aquarium. The 90 gallon has the same dimensions as the 75 gallon except it is taller. When choosing an aquarium, keep in mind how deep you will need to reach in order to plant or transplant. The 90 gallon might be too tall, depending on your arm’s length and desire to be up to your armpits when pruning. These are basically personal and aesthetic choices.

Ecologically, smaller aquariums are easier to throw out of balance than larger ones. For example, an excess dose of fish food can create an excess nutrient problem in a small aquarium faster than a large one. Still, you could grow aquatic plants in a plastic bucket if you cared to. In fact, I know of a number of folks that use “bucket gardens” for grow-out aquariums and holding aquariums for “extra” plants.

Almost any substrate that has a particle size of about 1 to 3 mm can work for a planted aquarium once the substrate accumulates a healthy amount of mulm, which is the “powdery” detritus that develops in a living aquarium. Standard epoxy-covered gravels will therefore work, especially if one adds some laterite underneath the gravel. What tends to work better right from the start (and for many, for the long term) is a substrate comprising highly porous material. A fired natural clay product like Flourite is an example, as is the manufactured product EcoComplete. Both of these are highly porous, which promotes good bacterial growth in the substrate and also allows for good ion exchange for the roots. Some of the porous substrates also are good long-term sources of iron and a few other minerals which aquatic plants need in trace amounts. Florabase is another example of a manufactured porous substrate. However, aquatic plants with very fine roots will be easier to plant and will more easily take hold in a finer substrate.

About 3 to 4 inches of substrate work well, as a rule of thumb. In a small aquarium, stay closer to 2 inches, simply because more than that looks too massive in a small box. In a large aquarium, as much as 4 to 6 inches isn’t a bad idea. In all cases, it is a good idea to bank the substrate lower in front and higher in back. This will allow deeper rooting by larger plants, which will be planted toward the back of the aquarium. Banking the substrate higher to the back also helps enhance the appearance of depth and perspective, which improves the aquascape. 

For aquatic plants that do not develop substrate root structures but instead cling to rocks, driftwood and other surfaces, the substrate matters less. Common examples are Java fern and the Anubias varieties. Virtually all aquatic plants are perfectly happy to get their nutrients from the water column, so nutrient levels are more critical than the choice of substrate.

A good idea for any hard-to-grow aquatic plants is the addition of carbon dioxide to the water. This will do about as much to improve plant growth as high lighting levels but without increasing risks of algae blooms. You can get the benefits of adding carbon dioxide whether you have a high or low lighting level. On the other hand, if you have a high lighting level, you should add carbon dioxide to help the plants keep up with the higher light levels and reduce the risks of algae blooms. Carbon dioxide can be added inexpensively with a homemade yeast reactor that feeds the carbon dioxide into the intake of a powerhead or canister filter.

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