Algae Control

Hair Algae & Nitrates


The “Pungent” Algae

I have no doubt that MANY, MANY of you have experienced the no. 1 scourge of the home aquarium – Hair Algae! They are hardy and resilient and pretty blasted frustrating! Even with 16+ years of experience, I too still run into an unruly clump or two every once in a blue moon.

Typically called “hair” algae because of its physical appearance, it is easily identifiable as it grows in fuzzy dark green hard to remove tufts (Bryopsis has a bit more form looking similar to a fern or feather) and found to manifest itself for no apparent reason. These tufts eventually expand and will envelope all available rock and corals if left unchecked. In addition to its appearance it has a somewhat undesirable smell and probably tastes just as good which is why no self-respecting fish will eat it. Some claim that species of the rabbitfish family, algae eating blennies (Lawnmover and Bi-color), or particular tangs such as the Naso Tang (and others from the Zebrasoma and Ctenochaetus families) may help keep small amounts culled. Other animals such as the Emerald crab (Mithrax spp.), Longspine urchin (Diadema spp.), Lettuce Sea Slug (Tridachia crispa) have been known to do well against various hair algae. However, if the outbreak is massive these animal remedies will not prevent the algae from spreading unless you understand what is causing it.

Its sudden appearance is theorized to come from either waste from newly acquired animals carrying the algae in their gut, or frozen food that may be carrying fragments, or more likely culprit, water in which newly acquired fish have been transported. It is very difficult to avoid the eventual contraction of an algae species unless one is very careful with acclimation of new animals. In some cases, a two week quarantine will ensure that new animals will have a chance to empty their gut of all possible algae fragments.

Species such as Bryopsis are especially difficult to remove once it is rooted and is one of the telling characteristics of this type of algae. Means of ridding your aquarium of it start with testing your water and keeping your water parameters under control (See corresponding article on water testing). Installing a dependable protein skimmer is paramount in the fight against waste and dissolved organics in your system which can elevate your nitrates. High nitrates are fuel for the fire when it comes to algae and your nitrates need to be kept at levels of less than 5 mg/l, preferably 0 mg/l. Practicing de-sedimentation, or dislodging detritus and organics, with a basting bulb or small power-head will assist you in this by keeping gunk from settling in and under rocks. Nitrates will leach into organics that have a chance to settle and concentrate and build up over time. De-sedimentation before water changes will ensure that this does not happen and will also give your protein skimmer a chance to be more productive. Also, if you have large patches of algae, preen as much as you can out of your aquarium before you change the water. Algae stores nitrates and by removing it will help you in the fight to lower them. Last but not least, water changes! If you find that you have high nitrates then you may have no other alternative than to change out large portions of your aquarium water. Never change more than 50% of your aquarium water as 10-15% of your beneficial bacteria live in it. If you have a freshwater aquarium, gravel-vac 50% of your gravel while changing the water. Do not gravel-vac the other half until 2 weeks have passed. You may change another 50% of the water after a couple of days.

One quick note, make sure you are not OVERFEEDING! By-far the most overlooked reason for high nitrates!

If you still can’t seem to get it under control consider trying a Sea Hare.

In the very near future we will be testing a new product for eradicating hair algae and will relay our findings once we’ve finished our trials. However, even if it is found to be helpful everyone needs to remember that any kind of treatment is only a band-aid and not the remedy. If you have an outbreak of any kind of algae, dinoflagellate, or cyanobacterium, testing will give you a profile of your aquarium and possibly the reason for whatever outbreak you’re experiencing at which point you can diagnose and take appropriate action.

The Sea Hare


Their common name, Sea Hare, is derived from their rabbit like appearance as well as their appetite for greens. Sea Hares  are in the order Anaspidea and the family Aplysiidaeare and are generally referred to as sea slugs.  There are many beautiful sea slugs which are not recommended for the aquarium as their dietary needs are either unknown or extremely difficult to replicate in captivity.  Sea Hares however are entirely herbivorous  There is one in particular, Dolabella Auricularia, that thrives in captivity and rapidly consumes hair algae.

Sea Hare

Sea Hare - Dolabella Auricularia

In an effort to test the Sea Hares reputation we placed one into a tank that was overcome with hair algae.  Anyone who has been in the saltwater hobby has one time or another accidentally introduced hair algae either on liverock or coral.  Hair algae as you know is extremly efficient at absorbing nutrients and regardless of your water quality the same conditions that make for a healthy environment for corals also provide algae with what it needs to grow.

Before Adding The Sea Hare

Before Adding The Sea Hare

If you have tried other options unsuccessfully take a look at the results of adding a Sea Hare.  It only took about 5 minutes for the Sea Hare to begin clearing the rocks and substrate.  We did notice that they prefer to stay near the substrate so you may want to lay a few pieces of liverock close to the bottom if you don’t see the Sea Hare reaching the top of the tank.

By the next morning virtually 1/5 of this 50 gallon tank was completely cleared of hair algae.  We do recommend adding some Trochus Snails as well to clean up behind the Sea Hare.  Think of the Sea Hare as a weed eater and your snails as the lawn mower.  They clean up what is missed.  The Sea Hare unlike a lot of other cleanup options will consume hair algae regardless of the length.  So don’t worry if you have algae over an inch long.

Here is a picture of the same tank 3 weeks later.  You will notice that many different kinds of Caulerpa are now thriving as they are no longer choked out by the hair algae.

After Adding The Sea Hare

After Adding The Sea Hare

The Sea Hare does not like a lot of currents so we recommend turning off your pumps at night which is when the Sea Hare will come out to feed (Except at first if they have been at the local fish store without food).

Their dietary needs are important to consider. They have a voracious appetite so we recommend planning ahead to either feed alternative algae fair once your tank is clear or to share your Sea Hare with other aquarists.  We have been feeding the Sea Hare a supplemental diet of Sally’s Seaweed Salad- Green Marine Algae, which he appears to really enjoy.

Our Disclaimer:

Over the years we have heard about their remarkable abilities but we have avoided them as there is a potential for Sea Hares to ink.  This ink is toxic, however there are varying accounts of the degree of toxicity. We have avoided purchasing Sea Hares in the past due to this potential.  However, by acclimating the Sea Hare slowly, providing high water quality and powerful filtration we feel this threat can be greatly reduced. Make sure you find a way to cover pump intakes as that is most likely going to be the biggest threat to your Sea Hare.

There are currently multiple locations which breed Sea Hares in captivity, however it is done so for medical research instead of for the aquarium hobby.  Scientists are currently studying Sea Hares brains which are a clump of nerve cells in an effort to understand more about our brains.

If you have experience with Sea Hares, please feel free to add to this article.

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