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Topic: Saltwater Aquarium Guide

Saltwater Algea Control

July 13, 2006
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Everything you need to know to control algae in Saltwater.

Control of algae is one of the goals of every aquarist.  How much algae is too much really depends on you, as well as the type of system you run.  Certainly it is too much when it endangers the animals you put in your system.  It can do this by “suffocation” (corals) or by oxygen depletion at night (fish).  Remember that no tank is completely devoid of algae, and it is natural to have some.  You just need to keep from being an algae farmer.  Algae come in two basic forms – micro and macro, defined basically by size.  Here’s a concise breakdown of various algaes and ways to control them.


The first algae you get is rust colored or brown, and it grows on your substrate, glass and decorations.  This is a diatom, which feed primarily on silicates from your source water, new substrate, or freshly mixed saltwater.  Just turn it over, cycle your aquarium, and be patient, it will subside with time.  If it doesn’t go away or significantly decrease after you have cycled than focus on silicate remover, as well as checking through the master list for algae control later in this article.  Main tips for control – use purified water, silicate removers, change salt mixes, and perhaps employ a blue cheek goby (golden head sleeper) or jawfish.


This is the stuff that grows on your glass and is typically green.  Use turbo snails to help eat it, and if you are scraping once a week or less to control it, you’re doing okay.

Hair Algae:

Its green and fine, and can really bum you out.  Refer to the master list.  Best tips for control – keep nutrient levels low, skim til yer blue in the face, and buy some scavengers.


A more rare form of algae, and a little tougher to get rid of.  It looks thicker, tougher hair algae with a structure.  Don’t add this to your tank in the first place.  Best tips – not many things eat this – try a rabbitfish or a Foxface, as some will eat this, prune and scrape.  Also try the yellow eye tang.


Looks more like a plant to the untrained eye, and takes various forms ranging from grass to fern to grape to disk.  Prettier and less troublesome than most, it can still grow over and into your corals.  Easy to prune manually, make sure that you pull the rhizomes from their footholds.  Sell the stuff- it makes great fresh form of tang food.  One of the easiest algae problems to control.


This beautiful form of calcareous algae is not a nuisance.  If you grow to much of it, just pull it out and sell it, and pat yourself on the back for maintaining good calcium and alkalinity levels.

Slime Algae:

Red, brown, black and green, it grows in sheets and coats your substrate, and any other sessile object.  This is a very common problem, and it can grow quickly.  Primary causes are silicates and phosphates.  Best tips are to follow the entire master list, concentrating on good water and skimming.  In fish only tanks with acute (not chronic) problems, a tab of erythromycin per 50 gallons one time only will kill it in 24 hours.  Shut off your skimmer during this period and remove activated carbon or polyfilters.  Do not use repeatedly or you will kill your biological filter.  Do not sue in reef tanks.


Bubble algae looks like little green balls.  They can grow to the size of a large marble.  They can also grow in clusters.  Try to prevent introducing them in the first place, by cleaning of all rock before it goes into your tank.  Best tips- prune manually and use the world’s best kept secret, the foxface, which eats it far better than he only other reported muncher, Desjardin’s tang.  This is a tough one to get rid of.


Looks like brown slime algae that grows up in strands, and typically has small bubbles trapped in it.  Outbreaks can be sudden and severe, and damaging to corals.  Siphon it off, reduce photoperiod temporarily, reduce trace element additions, and crank your pH to 8.6.  the pH must be maintained high continuously for it to work.

Kelp and Sargassum:

Actually plants are not very common, rarely seen as a problem.  Included just to be comprehensive.

Now that we have covered the basic types of algae, its time for “The master list of algae control!”  Follow every item on the list and chances are you will hit on a cure for your problem.


The Master List!

Different tanks have different root causes for algae problems.  Sometimes these causes are subtle, so examine each item carefully.

  • 1.      Patience – algae are a very successful group of organisms, and they won’t go without a fight.  Over night cures do not exist.  If at first you don’t succeed, try, try again.  Know that you are not alone – virtually everyone has battled algae at one point or another.  Even master gardeners pull weeds.
  • 2.      Good algae growth.  You can help control ugly algaes by cultivating pretty ones.  Coraline, halimeda and certain types of caulerpa are the only forms worth cultivating, along with the symbiotic algaes in the tissue of corals.  The reason it helps is simple.  Nutrients in your water will make something grow, so it may as well be pretty.  Sort of the way a healthy lawn deters wee growth.  Coraline algae inhibit the adherence of undesirable algaes.  Proper lighting, calcium, pH and alkalinity, trace elements and cycling are necessary to grow this stuff, as well as seeding your tank initially.  It is purple and pink and magenta and it is prettier than gray.  It grows slowly, but the old saying is to fight algae with algae.  Halimeda and Caulerpa at least have nice form and structure, as well as being easy to prune and sell.  Requires lots of calcium and iron respectively.  Symbiotic algae in corals qualifies as good algae.  If your rock surfaces are covered with coral tissue, it will absorb the light and nutrients, assuming both are maintained at the proper levels, high and low respectively.  Requires trace elements and proper calcium and alkalinity levels.
  • 3.      Minimize nutrient input, maximize nutrient output.  Not a new idea, but one of the tried and true. What it means is: don’t overfeed, have a fantastic protein skimmer, and don’t slack on water changes.  And vacuum the crud out of your gravel.
  • 4.      Don’t overfeed.  Every bit of uneaten food is broken down by bacteria into fertilizer for algae.
  • 5.      Change water and vacuum your substrate.  Gravity always works, and fish waste and uneaten food will accumulate in the gravel.  Remember, poop is nature’s fertilizer, so letting waste build up will provide an ongoing source of fertilizer for algae.  Plenum type systems may be excluded from deep digging in the gravel, just focus on the upper half inch.
  • 6.      Have a good protein skimmer, keep it clean, and keep it functioning properly.  Nothing exports nutrients more efficiently than a skimmer.  Think of it as bubbling fertilizer directly out of your system for you.  It you do everything on this list and still have an algae problem, you probably have an inefficient or undersized protein skimmer.
  • 7.      Establish your biological filter, and maintain its integrity.  In the absence of good bacteria converting nitrogenous wastes, algae will do it for you.  Yes, they can eat ammonia, nitrite, nitrate, phosphate and silicate.  In reef tanks, do not use an external biological filter, simply let your rock do it for you.  Trickle filters become nitrate factories, causing faster algae growth.
  • 8.      Use purified water.  This eliminates unwanted algae promoting nutrients.  Especially critical for those of us who have well water.  Purified water comes in three basic forms: distilled reverse osmosis, and deionized.  If you have to buy 5 gallons or more of distilled water a week, buy your own water purifier, it will pay for itself quickly.  Remember, performing water changes with water containing bad nutrients is like replacing the oil in your engine with dirty oil.  A vicious circle.  Topping off with unpurified water is even worse, as you will just increase the amount of dissolved nutrients.  This happens because just the water evaporates, leaving behind all the contaminants that came with it.
  • 9.      Reduce or temporarily discontinue the use of trace elements.  Over use of these will help your algae grow.  Keep using any buffers or calcium supplements however, as proper pH, alkalinity and calcium levels will help to increase coraline algae growth, reduce bad algae growth, and to some extent increase the efficiency of your skimmer.  Do not use liquid foods that are meat based, as they are known not so affectionately as liquid algae grower.  Most corals that eat can be spot fed with an eye dropper or baster, and most fine filter feeders can be fed with vitamins or phytoplankton, with better results than liquefied shrimp.
  • 10.   Use proper lighting.  Bad algae typically likes the red end of  the light spectrum, so don’t use cheap hardware store bulbs.  Keep your photoperiod to 12 hours or less, keep your bulbs fresh (replace every 6-9 months) and use enough intensity.  For fish only systems, either use low lighting levels, or grow hair algae on purpose to feed your fish.
  • 11.   Use the proper substrate.  Dolomite is out, so are the fresh type gravels.  Crushed oyster shell and crushed coral are okay, but the best substrate is aragonite or live sand.  If using the sand, keep your thickness down to half an inch, and make darn sure that the sand is not silica based, or you will never get rid of slime algae.  If using gravel, no thicker than two inches.  If using a plenum, it must be three and a half inches or more thick and of proper size.  Another idea is to remove a portion of your substrate from time to time and replace it with fresh stuff.  Focus on the top layer as this is where most algae will adhere, and this is where a lot of phosphate will be locked up.
  • 12.    Use good quality chemical absorbents.  Activated carbon, phosphate remover, silicate remover, poly-filters and ion-exchange resins will all remove algae promoting nutrients.  By themselves, they will not control a problem, but using them along with everything else will help you through acute periods.
  • 13.   Scrape, prune, siphon and twirl.  Scrape your algae off the glass.  Prune your algae by hand.  Siphon your algae out directly.  One trick here is to attach a small diameter plastic pipette cut at a 45 degree angle to your siphon tube and actually remove the algae directly from your rock.  This technique is especially helpful for hair, bubble and dinoflagellates.  Twirl – this works for hair and bryopsis algaes only when they have grown fairly tall.  Use a filter brush or airline size rigid tubing.  Think of twirling your fork in spaghetti and you’ll get the idea.
  • 14.   Keep mechanical filters clean.  They will trap algae, and increase the efficiency of removal.  Try cleaning your mechanical filters a half hour after the scrape, prune and twirl bit. This is when your mechanical filters will be full of algae, so remove it before it breaks down and re-enters your system.
  • 15.   Scavenger animals.  Yes, there are critters out there that will be happy to keep your tank cleaner for you.  Turbo snails, blue and scarlet hermits, algae blennies , tangs, urchins, jawfish and blue cheeks, and the best kept secret, the Foxface.

    Snails include the astrea, mexican turbos and the turbos from far east Asia.  All are good micro algae eaters, as well as eating diatoms and short hair algae.  They won’t eat bubble, bryopsis, caluerpa, halimeda, slime or dinoflagellates.  The later two may be toxic to turbos.

    Hermit crabs include small species such as the blue claw and scarlet reef types.  Do not use large hermits in reef tanks.  They may occasionally kill snails for their shells.  If you don’t have much bad algae and they are hungry they may eat coralline algae.

    Algae blenny, eyelash blenny, lawnmower blenny, a.k.a. salarias spp.  These cute little guys live to clean algae off your rock and glass and substrate.  They put a chameleon to shame with their ability to camouflage themselves.  You can look right at them and not see them until their eye moves!  They have a face like a walrus without the tusks.

    Tangs are a large group, many of which will control hair and caulerpa.  The pointy nosed ones (zebrasoma) are better algae eaters than the more blunt nosed ones.  They are pretty and generally reef safe.  Please do yourself the favor of quarantining these guys before putting them in a tank with inverts.  There have been reports of Desjardin’s tang eating bubble algae, but don’t bank on it.  Some tangs will eat bryopsis, but this seems to be luck of the draw, try the yellow eye.

    Urchins will eat lots of algae, but they will also bulldoze, eat coralline, and small sesile inverts of all types.  Use them only in tanks that have extreme problems, or fish only systems, or where there is not much for them to eat except algae.

    Jawfish and blue cheeks don’t really eat algae, but they continuously turn your gravel over to prevent diatoms and micro algae on your substrate.  Be careful, they are jumpers!

    The world’s heavyweight champion of algae eaters, the Foxface  (Lo vulpinis).  Yellow with black and white face and a pointed nose, this fish has venomous dorsal spines, so handle carefully.  They will eat virtually any algae, starting with the prettiest – some blue, purple and red macroalgae for example.  When that is gone, they move to all forms of caulerpa, sargassum and kelp.  Then it’s the hair algae, which is cropped short enough for snails and hermits to finish.  If all other forms are lacking, then they will eat bryopsis and bubble algae.  Yes, bubble algae!  The author has seen a 70 gal with severe bubble algae infestation completely cured of valonia within months of introducing one of these functional friends.  They are reef safe.  They will not eat slime or dinoflagellates.  They will try to eat diatoms, but don’t have the correct mouth structure to be effective.  Oddly, some aquarists have reported that the Foxface didn’t do their jobs.  These aquarists possible fed too much, didn’t have enough patience, or had a hopeless problem.  Rabbitfish are relatives of the Foxface that may also eat algae.  In general, the Foxface deserves the gold medal in the algae eating Olympics.

Ultraviolet sterilizers – these can help to control algae that reproduce with spores in the water column by zapping spores as they pass through it.

Ozonizers – these help with algae control by oxidizing organic wastes, directly killing algae spores, and generally raising your redox potential-cleaner water means less algae.

Learn to recognize the various forms of algae so you know what you’re dealing with. Follow the master list, be patient, and you can overcome the battle with algae.  Then you can work less and enjoy more!  Good luck!

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