Trials and Tribulations of a Reef Aquarium: A Brief Primer on Algae: the Good & the Bad

Algae: Friend or Foe?

I thought all algae was bad in aquarium-speak. But I spoke too soon. Normally, we try to get rid of algae in our aquarium. Algae is not necessarily bad, in and of itself; however, it is a sign that you have an underlying problem. In other words, algae is the symptom, not the disease. Things like: Light, Phosphates, and Nitrates promote algae growth. Small, frequent water changes, an excellent filtration system, good water flow, and a good clean-up crew (crabs, snails, shrimp and some fish) are excellent ways to control algae growth.

Keep in mind there are a myriad of different types of algae: brown, green, red. Diatoms, cyanobacteria (red slime algae--although not an algae at all), macroalgae, green hair algae, and coralline algae. The one thing they all have in common? They all photosynthesize from light. Most also feed on nitrates and phosphates as well. The similarities stop there. Some are eukaryotic; some prokaryotic. Some single-celled; others (macroalgae) are multi-celled (like kelp and seaweed). Some types are desirable, some are not. In other words, it's like weeding your garden. You weed out the ones you don't want and try to propagate the beneficial ones.

Coralline Algae:

For instance, encrusting coralline algae, introduced on live rock, gives saltwater aquariums their gorgeous color. I love all the bright pinks, reds, and whites covering my live rock! Because coralline algae incorporate calcium into their hard skeletons, like coral, it's important to have proper calcium levels in your tank to stimulate coralline algae growth. Coralline algae can help cement your live rock together, providing a strong foundation for building a reef.

Cyanobacteria (Red Slime Algae):

This is not an algae at all but in fact, a bacteria. Cyano is an undesirable pest in your aquarium. Things like light, phosphates, and nitrates promote its growth, like most algae. You have to give the cyano some respect though--it's one of the oldest lifeforms on the planet, dating back to 3.5 million years ago. Also, some scientists think that plants got their chloroplasts from cyanobacteria via a looong evolutionary process called endosymbiosis. In fact, the oxygen produced as a byproduct of cyano's photosynthesis may be the reason why we have blue skies on our planet. Don't be deceived by the name either; cyano can be blue, green, black, or red in color.

Diatoms (Brown Algae):

These brown, single-celled organisms are one of the first signs of life in your new aquarium as its cycling. They feed off of silicates found in the substrate and form an unsightly brown slime over everything. Luckily, as quickly as they grow, they die quickly too. They can easily be stirred up and wiped away. Keep in mind that these simple organisms make up the photosynthetic part of plankton (phytoplankton) and feed zooplankton (copepods).

Diatoms--very pretty under a microscope!

--not so pretty in your aquarium

Blue-Green Algae (Chlorophyta):

This is the most common type of algae in our aquariums and often the picture we get in our heads when we think of algae. Slimy, green, and hairy, green algae looks similar to a green swamp monster. This is also the type of algae you want to leave in patches to feed your tang and other algae-loving critters!

--Blue-Green Algae under a microscope

--an aquarium overgrown with Blue-Green algae

Macro Algae:

You will actually find yourself buying algae at one point from your LFS. I did. I added the seaweed-looking green stuff to my refugium. They clean up nitrates and phosphates like no one's business and provide a safe harbor for propagating tiny beneficial critters like copepods to feed my tank. Basically, I'm making plankton. Lots of fish eat it too. There are a myriad of different types, all different shapes, sizes, and colors. I recommend a variety. They are the plants of the saltwater world.

Kelp--the ocean's largest macro algae

Types of macro algae available for purchase at your LFS:

Take Home Message:

Keep in mind that algae is going to be an inhabitant in your saltwater aquarium, whether you like it or not. And, just like you don't want that xenia coral you put in your tank to take over the entire system, you also don't want a showcase algae aquarium. So keeping algal growth in control is important. But be careful not to go too far the other way and "sterilize" your tank. A healthy tank has some algae growth. Lots of little organisms (and some of your fish...like tangs!) love to eat the algae. So make sure to keep some algae pastures to keep your aquarium tenants happy.