Mark Martin on Controlling Algae with Algae
Mark Martin is the Director of Marine Ornamental Research at Blue Zoo

For the purposes of this discussion, there are three main groups of algae with which marine aquarists are generally concerned. They may be considered nuisance algae, ornamental algae and refugium algae, and understanding the role of each will lead to a beautiful display tank and low levels of excessive nutrients in the system overall.

All algae take up nutrients—that’s a critically important concept to understand. If you call me and say “Hey, I have an algae problem,” I’ll probably tell you, “No, you have a nutrient problem.” Why? Because when someone says they have an algae problem, they are usually referring to nuisance algae in their display tank, and the nuisance algae in their display tank is thriving because there are plenty of nutrients in the system. Remove the nutrients, and you usually get the nuisance algae under control. Make sense?

Often, however, when I tell people who call with an algae problem that they have a nutrient problem, they respond by telling me that they don’t have a nutrient problem. Why don’t they think they have a nutrient problem? Because when they test for nutrients, the test shows none. “Ah,” I say, “but that’s because the nutrients are being bound up by the nuisance algae before you can test for them.”

Now this last point is an important point—the fact that nutrients can be bound up in algae. Why? Because if you understand that nutrients you want to export from your system can be bound up in algae, then you understand that algae can be used to assist with nutrient export. Does this mean you want to grow nuisance algae in your display tank? Of course not—that’s the problem we are trying to solve. While it may be appropriate for some aquarists to grow certain slow-growing, ornamental algae in their display tanks (e.g. Halimeda), these algae are not efficient enough to be used for nutrient export, and this is why we turn to the third group of algae—refugium algae.

A refugium is an attached tank (plumbed to your display tank) in which you can cultivate fast-growing algae such as those from the genus Chaetomorpha. Because the refugium is separate from the display tank, you can easily cultivate and control the growth of algae in the refugium. You can also readily cut back the rapid growth, which in turn is a means to completely export the nutrients bound up in the algae from the system.

So why can’t you just grow the algae in the display tank? Of course this brings us back to where we began. All of the fast-growing algae species like Chaetomorpha spp. will rapidly overgrow a display tank and, essentially, turn it into a refugium. That’s not what most people are after.

To review, if you have nuisance algae in your display tank, you have a nutrient problem (even if you don’t detect excessive nutrients by testing). If you have a nutrient problem, you must address the root issue that is causing the excessive nutrients or find a way to export nutrients more efficiently from the system (or both). In addition to good husbandry practices and effective filtration, growing the right algae in a refugium can be an excellent way to export nutrients from the system and keep nuisance algae in check in the display tank.

Have a question for Mark? Please e-mail him at customerservice@bluezooaquatics.com.

Published 27Feb 2009. © Blue Zoo Aquatics