An old liverock of mine covered in red, purple and green coralline algae.
Almost everyone first getting into the hobby is obsessed with having coralline growing all over their rocks. They buy all sorts of additives like Purple-Up etc to try and promote it to grow in an attempt to add a bit of color to their tank. It isn't until they find themselves having trouble looking into their tank due to the glass being completely covered with coralline that they find their love for coralline turning into a dislike putting it in the category of a "nuicance". So what exactly is coralline and what exactly is it's purpose? Does it even have a purpose? let's take a closer look at it and see what we come up with.
Put simply, coralline algae is a type of algae that has a calcerous based skeleton. A more scientific definition coming from The Encyclopedia of the Earth is, "Coralline algae are calcifying red algae, which have a hard skeleton resulting from the precipitation of calcium carbonate within their cell walls". Coralline can grow in waters as shallow as a few inches deep to depths as deep as a couple hunderd feet and is pretty much found anywhere in the world meaning, that it will grow in warm temperate climates as well as in places where it is very cold. They come in a wide array of colors like purple, pink and green we typically see in our aquariums, to yellow and even blue's from what I have read. In addition to that, coralline will grow under very intense lighting as well as under very dim lighting which is why you will see tanks that are running either high wattage metal halide lighting (for example) covered in coralline algae as well as you will see the same thing happeneing in tanks that uses low wattage VHO's or pc lighting. Coralline also falls under two major groups:
Articulated - These are the branching type of coralline that is somewhat flexible in nature (ie like joints of your fingers as described by Boomer) and grows almost like certain plants or trees similar to cedar or bamboo (just to give a few comparable examples). This type of coralline you typically don't see in an aquarium.
Non-Articulated - These are the crusty type that we typically have in our aquariums that grow on the surfaces of the glass, rocks, or on pretty much any surface in our tanks if you let it.
Image Copyright © Malcolm Storey, 2008, BioImages - Virtual Fieldguide (UK). Some rights reserved.
Image is of one of the many types of articulated coralline algae's you will find in the wild
So, does coralline algae have a purpose or is it just one of those things you can either do with or do without? Well, to our surprise, coralline actually is very important to the oceans and even to our aquariums. Let's take a look at a few of these things...
Food Source - Certain marine life feed on coralline algae which include things like sea-urchins, chitons/curbs, some crabs, some snails etc (just to name a few). This is one of the reasons why you will see people suggest adding a sea-urchin or two to an aquarium where coralline has gone crazy in an effort to try and control it somewhat.
Micro habitats- The group "articulated coralline" we discussed earlier actually forms microhabitats in the wild for invertebrates to hide in which protects them from being preyed upon by fish. According to wikipedia, it was discovered that in Canada, certain invertebrates like sea-urchins, chitons and limpits would suffer 100% mortality due to fish predation had they not had the "knobby and undercut coralline algae" to protect them.
Reef Structure - The non-articulated coraline algae we typically have growing in our tanks are very important to reef structure. Without it, the reefs would have a hard time forming an actual structure as it is the coralline that actually "cements" the reef structure together. Pretty cool!!
Coloration - One of the most appealing attributes of coralline is the beauty and coloration it adds to our tanks (ie if it is kept under control and not allowed to take over every single surface area in our tanks LOL). Thanks to coralline, we don't have to look at dull brown or grey rocks, but rather rocks covered in the pretty shades coralline comes in. I think this is where the fascination hobbyist have with coralline comes from.
Out of our aquariums - According to the Encyclopedia of the Earth, coralline algae is used for various economic purposes such as a soil conditioner, treatment for acid drinking water, animal food additive and pharmaceutical products. Bet you dodn't know that!! Well me either till I read it LOL!
Un-fortunately, unlike other "algae's" coraline will have to be introduced into the tank and will not just grow on it's own like diatoms seem to do...Go figure!. There are several techniques and methods people go about introducing coralline into their aquarium which includes the obvious, adding liverock which has coraline growing on it already or adding coralline scrapings from someones tank, the ocean or where ever into your tank. The best way to go about this proceedure (ie adding coralline scrapings to a tank) would be to turn of your skimmer and everything else in the tank besides your pumps that you use for flow. Once you do this, toss the scrapings in the tank and allow the flow to spread it everywhere. After a few mintues, you can then turn back on your skimmer and pumps when you feel the scrapings have been evenly distributed around the aquarium. I have personally done this at one point to seed one of my aquariums which worked like a charm. I obtained the coralline scrapings off of rocks, broken glass and even shells found in water as shallow as 3-4ft deep.
To promote the growth of coralline algae, you will need to have really good water chemistry. What this entails is having your calcium, alk and magnesium all in balance and as close to NSW as possible. Calcium should be kept in the 420 mg/L range (give or take a little), alk around 9 dkh, magnesium about 1200-1300 and salinity around 1.024. In addition to this, it is said that coralline doesn't do well where phosphates are present as well as nitrates so you will want to make sure that these levels are kept minimal (like 5 ppm at most to O) if at all possible. Coralline algae almost acts more like a coral than an algae as it requires basically the same thing's as corals do to thrive and grow including light. Speaking of light, as I mentioned earlier in the article, coralline will grow under either high intense lighting or low lighting. All that lighting will determine is which type (and even possibly color) of coraline will grow in your tank as some prefer low lit aquariums whereas others prefer more intense lighting.
A prime example of good water chemistry displayed in Charlie's tank. Note the great coralline growth!
Having coralline growing in our aquariums is one of those things you can either love or hate. In my personal opinion though, where our aquariums are concerned, unless you have certain organisms like sea-urchins that require coralline as a food source, then I don't think it something that you necessarily need in order to have a successful aquarium. I look at it as just one of those things that adds a bit of color to our aquariums which is something we all desire...To have a tank that is visually appealing. Too much of it though, and it can become a nuicance and can actually take a way from the beauty of your tank making things look even more un-natural in some cases. To add to that, the fact that coralline uses calcium, alk and mag to grow, will mean that you will have to make sure you stay on top of testing your water regularily so that if any adjustments need to be made in your dosing of calcium, alk etc, that they are adjusted in an effort to ensure that you always maintain good water chemistry as your corals will require these same trace elements as well to survive. The last thing you want to do is to rob them of these things.
So with that said, having coralline growing nicely in your aquarium can be viewed as a good sign that your tank is pretty healthy and has ideal water chemistry so don't think of it as a bad thing or a curse. All this means is that you are doing things right and it will be totally up to you from there if you will allow it take over your tank or you control where you have it grow.
The article can be discussed HERE