Selecting Plants for Your Saltwater Aquarium

Selecting plants as a decoration for a saltwater aquarium can be somewhat tricky since, in most cases, they're not typical "plants" at all, but rather algae. Algae have gotten a bad rap, particularly from freshwater hobbyists who lunge for an herbicide with the mere mention of the word. But algae are nothing more than non-flowering plants that usually grow in water. They are extremely hardy (among the oldest life forms on this planet) and require only good water quality and light, with nutrients being supplied from the waste products of your pets.

For the saltwater hobbyist the distinction between bad and good algae lies between micro-algae, which are only seen once they are growing out of control, and macro-algae, which grow in various shapes and forms. Micro-algae can wreak havoc in your system, but macro-algae can add a nice "natural" touch to your aquarium.

Algae Improves Water Quality

These "plants" are easily thinned or weeded and can help improve the water quality in your tank by taking up nitrates and aerating water. If you have fish or invertebrates that need some vegetable matter in their diet, macro-algae provide a feeding station and hiding places as well.

Because algae don't flower and thus have no seeds, many reproduce either through clipping or a release of spores, which in a tank most often get cleaned out by the filtration system. Algae typically don't need any help once they get going: You'll find you need to prune them eventually, so reproduction isn't commonly an issue unless you've had a die-back. Algae terminology is a little different from plants. What would be identified as leaves in plants are called blades, stems are called stipes and roots are called holdfasts.

Green algae are photosynthetic and need lots of light; many calcareous algae, also a type of green algae, begin as green in color but turn white as they age and calcium carbonate encrusts on their blades and stipes. Red and brown varieties can do fine in low to medium light. Green algae grow fast in brighter light, slower in dimmer lighting, however the red and brown varieties grow slowly regardless of the light levels beyond their normal requirements.

Several popular varieties of macro-algae are available from stores. Some require a little more pruning than others. If you have coral in your tank, you need to make sure that as the algae spreads it doesn't block out living space and light and overgrow your invertebrates. Once algae has taken hold of your corals, it's difficult to get them out, embedding their holdfasts into the coral rock.

Should you decide to add macro-algae to your tank, be aware of "die-back," in which algae turn white and die, in some cases, overnight. This is usually caused by poor water quality, or sometimes just "old age" of the plants. When this happens, the water can turn milky-white as all the toxins are released into it and kill your pets in less than a day. If you detect any sign of such deterioration, be sure to remove the algae immediately or the section of it that is dying.

Varieties of Algae

• Caulerpa sertularioides, a fern-like algae once known as C. mexicana is probably the most common macroalgae to keep. It grows quickly and can get out of hand if not pruned on a regular basis. A close relative C. prolifera, as its name implies, is also a quick grower, but just as easy to prune.
• Caulerpa racemosa, also called grape algae for the way that it looks, is a macroalgae that encrusts itself on rocks. It grows in little bubble-like clusters. If you have coral, it's a good idea to stay away from this algae unless you watch it carefully, since it will easily grow over sessile invertebrates. Once this algae has taken hold on a rock, it is quite difficult to remove.
• Caulerpa cuperessoides is also known as cactus algae for its cactus-like blades. It doesn't grow as quickly as the aforementioned species and is easy to control.
• Penecillus capitatus, or paint-brush algae, is a calcareous algae that looks like a large make-up brush that sticks out of the substrate. They are relatively slow growers and don't require a lot of pruning. However, watch out as once they become too encrusted with calcium carbonate, a normal process that occurs as the algae grows, it can no longer photosynthesize and will eventually die.
• Halimeda opuntia, also known as cornflake algae because its blades look like small cornflake cereal, is also a calcareous algae that too will turn white with age as limestone encrusts on it. Like paintbrush algae, you must watch for signs of impending death and remove some of the white flakes that are shed. If you're a first-time grower, avoid both of these calcareous algae; they require a little experience to keep successfully.
• Udotea spinulosa is a calcareous algae that resembles a fan and unlike Halimeda or Penecillus, doesn't pose as great a die-off threat. This is, in part, because it is a very slow grower. But be warned, this algae will die at the slightest water-quality compromise, so your tank must be well-established and stable to keep this macro-algae.
• Halymenia spp. and Gracilaria spp. are highly-prized red algae. They grow much slower than the Caulerpa species and don't require frequent pruning. They are also decorative and will add a nice touch to just about any saltwater aquarium.

Live rock commonly has pink encrusting algae and foraminifera on it, both calcareous in nature. Reef keepers love it because it isn't that prolific a grower and adds a little more color to the tank. If you have pink encrusting algae, almost inevitable in most reef tanks, you may have to add a little extra calcium.

Try to stay away from highly prolific growers such as Bryopsis spp. and Seriatopora spp since both will quickly overgrow anything not moving in your tank. For algae-only tanks, these can be a decorative addition.

The only potential problems result in either poor care of these plants or an overgrowth, which can be easily controlled by merely removing them.