Algae Control

Algae proliferates naturally in the saltwater aquarium and without adequate algae control it can and will overrun our saltwater aquarium.

To the saltwater aquarium hobbyist,  there are just 2 types of algae — desirable algae and nuisance algae.  And both require enough light, nitrates, phosphate and nutrients to fluorish.


Microalgae are undesirable algae.  Their tiny structure makes them difficult to remove manually and their tendency to proliferate rapidly in high nutrient environments makes them the scourge of many an aquarist.

algae control

Nuisance hair algae smothering zoanthids

Mention microalgae to experienced aquarium keepers and most will immediately think of hair algae.  Hair algae spreads rapidly in an aquarium with high nitrates, phosphate, silicates and dissolved organics.

Hair algae will not just spread on the live rock in the aquarium.  Without an adequate algae control regimen to remove them, they will also smother corals, depriving them of light and preventing photosynthesis.

A hair algae dominated saltwater aquarium is a sad sight indeed!


Generally thought to be desirable, macroalgae play an important role in the saltwater aquarium.  Like microalgae, macroalgae absorb nutrients like nitrates and phosphates from the water, ‘scrubbing’ the water clean and improving water quality for our marine aquarium inhabitants.

But unlike microalgae, macroalgae are more easily controllable when they spread in the aquarium.   Because of their larger size, algae control in this case would just mean simple pruning when they get out of hand.

Macroalgae are also quite attractive with their various shapes, colors and forms.  Whether or not macroalgae are allowed to proliferate in the main display tank is a matter of personal preference.  Most aquarists will allow a small amount of macroalgae to spread, adding to the diversity of species in the main display.

Another school of thought is to limit them to a separate refugium in the sump where they will perform their useful role of nutrient control, out of view of the main display.

Algae Control Methods

Algae Control With Water Changes

If you have a microalgae problem, perform 5 gallon water changes every 3 days, siphoning out as much algae as you can each time.  Scrub the algae off the rock with a long handled brush for hard to reach areas.  In severe cases, remove the upper rockwork and scrub the live rock in buckets filled with aquarium water.  Do not use freshwater as this will kill off the beneficial bacteria and organisms in the live rock!

Aqua Gloves are highly recommended!

Use a slim 1/2″ vinyl tube to siphon out the algae as it detaches and floats around the aquarium.  The 1/2″ diameter will give you time to siphon out the algae without siphoning out too much water too quickly.   The 1/2″ tubing will not clog as easily as regular 1/4″ airline tubing.

I usually turn off the return pump to stop stray pieces of algae from entering the sump through the overflow.

The frequent regular water changes will also reduce nitrate, silicate, phosphate and nutrient levels in the water, effectively starving out the algae over time.  Algae control using this method will require persistence and perserverance to keep up with the water change regime as long as it takes to win the battle!

Algae Control By Reducing Feeding

Since algae thrive in water that is high in nutrients, the best way to limit their growth is by cutting back on their fertilizer — nitrates and phosphates from fish food!

Reducing feeding will limit the input of phosphates and nitrates into the aquarium as you are battling hair algae.   If you feed pellet foods, soak them in tank water for a half hour.  The soaked pellets will appear larger and your fish will likely consume every bit.  Larger soaked pellets will also give you a look at the actual amount of food you are putting in your tank!

I generally avoid flake foods for the saltwater aquarium as they tend to contribute to nutrients much more than pellets or frozen foods.

When using frozen foods like mysis shrimp, be sure not to add the juice from the thawed cube.  I prefer to thaw frozen mysis in a cup filled with a little tapwater.  Using a fine sieve, I strain the water away before feeding the mysis to my fish.

Herbivorous Grazing Fish And Invertebrates For Algae Control

Fish like the various species of tangs and rabbitfish rapidly make short work of hair algae and are useful allies in algae control.  But again, this sometimes depends on the appetite preference of a particular fish.  One of my yellow tangs for example, refuses to graze on hair algae, preferring soaked pellets, mysis shrimp along with the occasional nori or seaweed.

Invertebrates like herbivorous hermit crabs are also good at cleaning up algae.  Their only downside is that hermit crabs tend to topple over rocks!

Algae Control By Removing Phosphate And Silicates

Using good phosphate adsorbing media like Rowaphos will greatly help in algae control.  Rowaphos also removes silicates, another cause of rampant microalgae.  You will have to run double or even triple the recommended dosage of Rowaphos in a phosphate reactor if yours is a severe algae problem.

To check if enough Rowaphos is being used, test the level of phosphate in the water coming directly out of the reactor.  It should read at zero or very near zero.  If the reading coming out of the reactor is the same as the phosphate level in your main tank, you’re not using enough Rowaphos or its time to change out the Rowaphos media.

Algae Control By Limiting Aquarium Lighting Duration

Cutting back on the lighting schedule is another way to control nuisance algae.  This method works well on fish-only tanks.  You can cut back on your lighting schedule from the usual 10 hours a day to 4 hours a day over the course of 2 weeks to a month for example.  A more drastic measure would be to turn off the aquarium lights entirely for 3 or 4 days, allowing only ambient light from the room.

But if you have light-loving corals or clams whose zooxanthalle require sufficient daily amounts of light, cut back on the lighting schedule to 4 or 5 hours a day at most for up to a week.  Monitor the appearance of the corals and clams in your saltwater aquarium daily if you choose this algae control method.

Read about desirable Coralline Algae

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