Aquatic plants exist in many of the biotopes that we may endeavour to recreate in our home aquariums.
In nature, these plants play an important role in the removal of nutrients from rivers and streams, as well as providing welcome hiding places for fish and fry. It makes sense that we utilise these benefits, cultivating aquatic plants to create aesthetically pleasing aquariums, at the same time improving water quality (leading to a visible reduction in algae) and providing our fish with a healthy, natural environment.
There are four main elements that aquatic plants require in order to thrive: water, light, nutrients, and carbon dioxide.
All plants require water in order to live, and this is obviously especially important for aquatic vegetation. Whilst most aquatic plants grow completely submerged under the water, there are some species that will also grow emersed providing their roots are submerged. Leaf shape may differ depending on whether the plant is growing in water or above the surface. There are also bog plants that may be cultivated in paludarium style set-ups, which will flourish if just their roots are kept damp. The majority of aquatic plants will do well in most types of water, as long as extremes of pH and hardness are avoided, although there are a number of species which will require specific parameters.
Plants make their own food in order to grow via a process called photosynthesis. The energy from sunlight is utilised by the chlorophyll in the leaves to produce glucose from water and carbon dioxide, also giving out oxygen as a by-product. In order to grow properly, aquatic plants require full-spectrum lighting that replicates natural daylight. Some plants will require more or less light than others, but most plants need 8-10 hours of light per day. Whilst there is a small selection of plants that thrive under low-moderate light conditions (the type of lighting that comes as standard in many aquarium kits), you will need to upgrade the illumination if you wish to keep a wider range of species, including many of the attractive carpeting foreground plants. Depending on budget, high output T5 fluorescent bulbs (which can be enhanced further via the use of reflectors), metal halides, or the latest energy-efficient LED lighting systems are all suitable for cultivating your aquatic plants. Stronger lighting will help to encourage red pigmentation in many stem plants, although it should be noted that with increased light levels, it is important to maintain optimum carbon dioxide levels alongside.
Aquatic plants require various nutrients if they are to flourish. Macronutrients are nutrients that plants need to consume in large quantities, such as nitrogen, phosphorous, and potassium. Micronutrients such as iron, magnesium, and manganese are required in much smaller amounts, but nevertheless are important for plant growth and health. Although tap water does contain a number of nutrients and minerals, many of these are quickly used up or else are present at levels too low to be considered of major use to plants. Some macronutrients will come from fish waste once it is broken down by the filter bacteria, but this will not be enough to sustain the plants and they will need to be supplied with quality fertilisers (containing both macro- and micronutrients) on a regular basis. Liquid additives are convenient and easy to use, and can be added just after performing a partial water change. Additionally, substrate choice can make all the difference.
Many substrates are quite large (over 4mm) and allow water to pass through easily; unfortunately though, water flowing through the substrate can also remove a large number of useful nutrients from the plant roots. A finer grade substrate (1-2mm) such as aquarium silica sand will allow a moderate amount of water movement, stopping the substrate from stagnating, but reducing the amount of nutrients lost. To further improve the substrate, a nutrient-rich porous planting medium can be mixed into the lower layers for the plant roots to find. Some modern planting mediums can be used on their own as a standalone substrate too, providing both nutritional value and an attractive base to compliment your plants. Alternatively, if it is too late to change your choice of substrate, plant fertiliser tablets are available which can be pushed down into the substrate near to the plant roots as required.
Carbon dioxide (CO2)
Carbon dioxide is essential for the growth of aquatic plants. Without it, they are unable to utilise the light and the nutrients in the water for photosynthesis. There will already be small amounts of CO2 in the aquarium as it is a by-product of fish respiration and gas exchange at the water’s surface; however, for aquariums with larger numbers of plants, this CO2 will be quickly used up and there will not be anywhere near enough available for all the plants to photosynthesise and grow. Low levels of CO2 in the presence of strong lighting and good nutrient levels can also lead to nuisance algae, so it is important to get the balance right. You can increase the amount of CO2 in your aquarium by using a CO2 injection system. Introductory kits such as simple fermentation canisters offer an economical choice for beginners. However, pressurised systems provide a more precise control over the amount of CO2 being released and allows for the CO2 to be switched off at night using a magnetic solenoid valve. During the hours of darkness, it is unnecessary to supplement with CO2 as the uptake of the plants is much reduced. Using a plug-in timer in conjunction with the solenoid valve will provide a completely automated system. A word of warning though: CO2 can be toxic to livestock. Levels should always be kept below 30ppm (test kits are available), so be very diligent about not adding too much. Bear in mind that some species are more susceptible to intoxication than others, particularly those from oxygen-rich surroundings such as hillstreams and fast flowing river rapids, so do some research and choose fish that are appropriate for this type of environment. CO2 fertilisation has pretty much revolutionised the planted aquarium hobby. With the addition of CO2, cultivating the incredible lush aquascapes we see in books/magazines and on social media can now become a reality for everyone.
Aside from the issues that riverine fish will have with CO2 injected tanks as mentioned above, other considerations must be given when selecting livestock for the planted aquarium. Many common fish such as barbs and larger gouramis are voracious plant eaters, and others, including many cichlids, may dig in the substrate and uproot plants. Ideal species could include small, peaceful shoaling fish, such as tetras, rasboras, and blue-eye/forktail rainbowfish, together with dwarf suckermouth catfish (Otocinclus spp.) and nerite snails to control algae without damaging the plants. Whilst the exquisitely coloured dwarf shrimps (Caridina and Neocardina spp.) have become very popular for nano tanks, they are not suitable for tanks with CO2 injection. They do, however, make ideal residents for the low-tech planted aquarium where CO2 is not in use. Maidenhead aquatics are happy to cater for the plant-enthusiast's needs and stock a wide range of associated dry goods online including lighting systems, substrates, fertilisers, CO2 sets, and test kits, with many more products available in-store. Some stores also offer a CO2 re-fill service. As well as equipment, we receive regular deliveries of quality live plants from our growers in Holland and elsewhere. We can obtain many other varieties on request by placing a special order with our suppliers, so please don't hesitate to ask if you are trying to source a particular plant species.
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