Beautiful Encrusting Algae But There’s A Small Downside

Marine aquarists try very hard to create a beautiful aquarium – whether the system is fish only or reef that is the target. These attempts are generally successful and often the picture is enhanced by Mother Nature. Mother Nature obviously provides the ‘eye targets’, the colourful fish and corals.

In the aquarium are usually rocks – whether fish only or reef this could be to provide homes and also be decorative. Both, particularly reef, could be ‘living rock’ for biological filtration. This rock is normally interesting in shape and over time provides a base for algae growth.

At this point the assumption is that the aquarist has properly maintained seawater quality which in turn means that stocking levels are acceptable. It’s also assumed that lighting is adequate.

Encrusting algae, often known as coralline algae which is more accurate, is lovely. It can cover upper surfaces of rocks and make a real contribution to the overall aquarium picture. Often it is introduced to the aquarium on live rock from the dealer or another aquarist. Helpfully, ordinary maintenance seems to assist in its spread.

I’ve taken some photos from areas in my aquarium (I’m not an expert on photography so hopefully they’re adequate!). The heading photo has nothing to do with the subject, it’s just that my flame angel (Centropyge loriculus) cruised by and I couldn’t resist pressing the button.

The next two photos show interesting formations created by the algae as it grows. As is often the case there is beauty in the detail. There is much more in the aquarium that isn’t shown.



Ok, so what’s this downside that has been mentioned? There’s always a price to be paid for anything, and the price demanded for this algae is in an extension of maintenance. However, this isn’t much.

The algae not only uses rocks as a base, it’s quite happy to use glass. On the rear glass this doesn’t matter, and in my case the left hand glass can be left as well. However, the other viewing glasses need to be cleaned periodically. Of course this is already done to deal with the green stuff that accumulates but unfortunately a magnet cleaner doesn’t usually remove the encrusting algae. Therefore a razor cleaner is the best tool.

The next two photos show growth on a corner and on a horizontal glass pump support. Coralline algae seems to like growing in the corners of the aquarium – or at least it does in mine. Cleaning is not a problem with a razor but make sure the razor is sharp and also have regard to the silicone joints if there are any.



Calcium testing is normally carried out where there is a known need for it. There is another test that is generally beneficial particularly with a reef and that is alkalinity. I maintain my alkalinity at about 4.0 meq/l (it drops off slowly, I test at routine seawater changes) and this seems to benefit the encrusting algae – not only the coralline but other types present as well. Maintaining a higher alkalinity is considered to be desirable with a reef system but is not essential.

It has been mentioned that routine maintenance could assist with the spread of coralline algae. When the algae is being scraped off the glass it disperses into the seawater and this seems to generate further growth in other areas of the aquarium, though I have never seen any scientific or other confirmation of this.

One more concern has been raised in the past – does the coralline algae presence on live rock reduce the effectiveness of live rock filtration. Bacteria essential to the well-being of the livestock dwell within the rock so could seawater fail to reach the bacteria causing their demise followed by serious problems? ‘No’ has to be the answer. Though, as far as I know, there hasn’t been serious or scientific testing of this question there hasn’t been a reported failure of filtration, again as far as I know. There are marine aquarists far and wide who are delighted with the presence of the algae. Personally I’m also delighted and have never had a problem with filtration because of the algae presence.

  1. I agree. I love the coralline algae. It’s funny. When it first started growing, I thought it was bad and wanted to know how to get rid of it! I also think the green algae gets a bad rap. I like to think of it as “tang pastures”.

  2. Hi Rachel. Coralline algae can really up the beauty level in an aquarium. What a great way of looking at green algae too! Green algae isn’t ‘bad’, it’s the amount of it that could be. The green stuff has got a poor reputation as so many aquarists have trouble with it. This is unfortunate as some green algae can be very decorative too.

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