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Tangs and Algae

Any advice on the type of tang that would help my hair algae problem?

By Scott W. Michael

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Aquarium Fish International Magazine
Q. I hope you can give me some advice regarding tangs. I'm having a small problem with hair algae in my saltwater aquarium, and read that certain tangs can help reduce this algae problem. I have been interested in the powder blue tang, but have been told they are not very good eaters in captivity, they would not last more than a few months, and because they are costly, I should consider looking at a hardier type, like a yellow tang or a blue tang. I really like the sohal tang, but they are very costly, as are purple tangs. Any advice on the type of tang that would help my hair algae problem? Also, could this hair algae be caused from excess nitrates or insufficient lighting? The last time I had the nitrates checked they were at 20 to 30 parts per million. I've been having difficulty reducing the nitrates lately.

My aquarium is 50 gallons and I have about 30 pounds of Marshall Island live rock in it. My fish consist of a flagfin angelfish, a maroon clown, a small green damsel, a royal gramma and a yellow watchman goby. I do about a 10- to 15-gallon water change each month, and add only iodine and a strontium solution every week. I have only a small portion of crushed coral (size 10) on the aquarium bottom, and have been told that I would be better off leaving the bottom bare to reduce nitrates. Is this true? I would rather have some type of bottom substrate because it looks so much better.

A. Let's address your nitrate and algae problems first, and then turn our attention to the tangs. Although the nitrate level could be lower, it's not unusually high. You mentioned that you like having substrate on the aquarium bottom because it looks so much better. Well, so do I!

Try mixing some live sand in with your crushed coral so that the bottom is covered with approximately 2 inches of substrate. Also add some sifting gobies, like the orange-spotted sleeper goby (Valenciennea puellaris), to help keep the sand surface stirred (note: these gobies are great jumpers, so a top of some sort must be used to keep them in the saltwater aquarium). The organisms that live in the live sand, through the process of denitrification, can help bring the nitrate levels down.

If you add a tang to the saltwater aquarium you will have a pretty heavy fish load, which also equates to increased nutrient levels. I would invest in a good protein skimmer (you may have one, but you didn't mention it) and stop adding iodine (unless you also have corals in the aquarium). You should add kalkwasser to your aquarium to boost calcium levels and encourage coralline algae growth, which will inhibit the growth of microalgae. I would make partial water changes every month (about 15 to 20 percent of water volume) using deionized water, and also use deionzied water when topping off the saltwater aquarium as water evaporates.

Controlling nitrates, phosphates and dissolved organics can help make our fight against the green plague easier. There is no doubt that when there is a surplus of algal nutrients, this botanical pest grows out of control, but I believe herbivores are essential to keeping an algae crop in check.

For example, studies conducted on coral reefs that occur in relatively nutrient-poor waters have demonstrated that if you exclude herbivores from an area, algae grows like mad! This is an indication that the herbivores are very important in shaping the reef's algae communities.

Our problem is to find fish and invertebrates that will eat the marine algae that has gone amuck in our aquariums. This brings us to the first part of your question — which tangs are right for the job.

The Tangs
There are 72 different species of tangs, or surgeonfishes, and these can be classified into several distinct feeding guilds. That is, the fish are categorized according to the type of feeding behavior(s) they exhibit. These guilds are: the zooplanktivores, browsers on macroalgae, browsers on microalgae and grazers on microalgae and detritus.

The tang you need to obtain to help control filamentous algae is a species that browses on microalgae. For example, the yellow tang (Zebrasoma flavescens) feeds primarily on filamentous algae in the wild. It will also feed on some of these microalgae in the aquarium. Although you may consider it to be run of the mill, the yellow tang is one of the best fish for helping to control hair algae in the aquarium.

This does not mean one yellow tang can eliminate all the filamentous algae in a 50-gallon saltwater aquarium, especially if the rocks are already coated in the green stuff. But, this fish will assist you in your efforts to keep it under control.

The purple tang (Zebrasoma xanthurum) also consumes filamentous micro- and blue-green algae, as well as some macroalgae. Although pricey, it too is a good aquarium fish. The only drawback to this species is that it can be aggressive toward closely related fish or similarly shaped species introduced into the tsaltwater aquarium after it has become established in the aquarium. It's also susceptible to parasitic infections. However, it is not nearly as aggressive as two other species you mentioned, the powder blue surgeonfish (Acanthurus leucosternon) and the sohal surgeonfish (Acanthurus sohal).

In the wild, the sohal patrols territories on the reef flat and reef crest and excludes all other herbivores from its domain. The modified spine on the base of the tail fin is larger in this species than in most other surgeonfishes, and is used effectively to drive off intruders. In the aquarium it is often difficult for the sohal's enemies to avoid its wrath, and they may end up dying as a result of wounds inflicted by the spine!

Because this fish gets large (up to 16 inches in total length), and because it is extremely active, it should be kept in a big aquarium. I would recommend an aquarium no smaller than 135 gallons — a 50-gallon saltwater aquarium is definitely too small. This species also feeds on microalgae, but filamentous green algae is not preferred fare.

The powder blue is also a hellion that will attack closely related species or any fish the looks or acts like it (omnivores and herbivores). It only grows to 9 inches in total length, and I would recommend you house it in a 75-gallon aquarium or larger. I have never had a problem getting a powder blue surgeonfish to eat, but they often come down with external parasites, such as saltwater ich (Cryptocaryon irritans). In fact, I affectionately refer to most surgeonfishes as ich magnets!

As far as controlling green hair algae growth, the powder blue is not the best candidate for the job. It prefers filamentous red, filamentous blue-green and fleshy red algae.

One thing you should be aware of when keeping surgeonfishes is that if they are fed frequently their search image may change from their natural food to the introduced fare. If this occurs the individual may eat little or no algae and instead wait for aquarist handouts. This is especially problematic in an aquarium like yours in which you have other saltwater fish in the aquarium that have to be fed at least twice a day to ensure they remain healthy.

There are also saltwater invertebrates that can be used to reduce algae growth. For example, Astraea and Turbo snails are popular choices for controlling some algae species. For a 50-gallon saltwater aquarium I would introduce 20 Astraea snails and five Turbo snails and see what happens. Be aware that if algae supplies run short, some of the snails may die of starvation. There are also small, herbivorous hermit crabs that will crop filamentous algae.

In some cases it will be necessary for the aquarist to assist in the role of primary consumer (e.g., herbivore). This can be accomplished by plucking the algae off the rocks and out of the saltwater aquarium with your fingers, tweezers, a toothbrush or a siphon hose. This is especially true if the algae crop gets way ahead of the herbivores or if an algae species that is ignored by your herbivores grows in your aquarium.

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