Fish alone will not fix an algae problem
Algae grows when nutrients and light favor it, so grazers help but rarely solve the cause. If nitrate or phosphate is high or the tank is overfed, algae often returns. Fish are most useful as part of a plan that includes testing, water changes, careful feeding and good filtration. It is also worth knowing that in a tank where fish are fed generously, some of them graze less than you might hope.
Match the grazer to the algae
Different algae types are eaten by different animals:
- Film algae and diatoms: bristletooth tangs and some blennies tend to graze these.
- Green hair algae: some tangs and rabbitfish are commonly reported to eat it, along with some snails.
- Bubble algae: often difficult. Some rabbitfish and certain crabs are reported to eat it, but results vary.
- Cyanobacteria: generally not controlled by fish. It is usually a nutrient or flow issue.
Best algae-eating saltwater fish
- Bristletooth tangs (Ctenochaetus species), such as kole and tomini. Comb-like teeth are well suited for scraping film algae and detritus from rocks. Tomini tangs stay relatively small, while kole tangs need more room. Both generally need a longer tank, often 70 gallons or more depending on species.
- Yellow tang. A popular grazer of filamentous algae, but it needs a large tank and open swimming space, and can be aggressive toward other tangs.
- Foxface rabbitfish. Reported to eat hair algae and macroalgae. They need a big tank and have venomous spines, so handle them carefully with gloves and a net.
- Lawnmower blenny. A small grazer often recommended for mid-sized tanks. It tends to pick at film algae on rock and glass, but can starve once algae is gone, so be ready to supplement with algae-based foods.
- Other blennies. Several blennies graze algae, but diets vary, so check the individual species.
Many of these are also reef compatible; see reef safe saltwater fish for caveats on mixed reef tanks.
What eats hair algae?
Commonly cited hair algae grazers include some tangs, foxface rabbitfish, certain blennies and several snails and urchins. Results differ between tanks, and fish that are well fed may ignore it. Taking out the algae by hand and fixing nutrient levels is often more effective than relying on livestock alone.
Snails and other clean-up crew
For snails that eat algae in a saltwater tank, hobbyists commonly use turbo snails, trochus snails, cerith snails and nerite snails. Each prefers different algae and types of surface, and each has limits: turbos can be large and clumsy in small tanks, for example. Hermit crabs and urchins also graze, but may bother corals or other invertebrates in some tanks. Remember that a clean-up crew is not a substitute for maintenance, and that large fish may eat snails and crabs.
Tank size and compatibility cautions
- Tangs and rabbitfish are active swimmers and typically need long tanks. Small tanks are not appropriate for them. Large tang relatives such as unicornfish are covered in our unicorn fish diet guide.
- Several tangs may fight, especially in tanks that are too small.
- Check adult size and temperament before buying. Our guide to compatible reef fish can help.
- Make sure they will have enough to eat by offering nori and algae-based foods.
What fish will clean my tank?
No fish truly cleans a tank. Algae eaters trim algae, and sand-sifting gobies stir the surface of sand, but nutrient control still depends on water changes, filtration and not overfeeding. For one popular option, see our guide to the best goby for a reef tank, and for tank basics see saltwater fish care.