Diatom Algae

Algae! Now there’s a word that can raise very mixed emotions in a marine aquarist. Even if the aquarist is a newcomer to the hobby, if plenty has been read in research he or she will be aware of the dangers.

Of course not all algae’s are bad; in fact they could be the aquarist’s friend. There are many forms of decorous algae. Caulerpa is a larger form of algae that is often used by more experienced aquarists to reduce nitrate and phosphate, as it uses the nutrients for its growth which of course means that other nuisance algae cannot. When used this way it is usually kept in the sump under individual lighting.

The algae types that worry aquarists the most are green filamentous and smear algae. Filamentous green algae take the form of very thin strands which are close together and could be up to 8″ (circa 20 cm) long. If unchecked it could cover all the rock and sand. Smear algae, also known as blue-green algae (though it comes in more than one colour variation), properly known as Cyanobacteria, which is often a dark reddish brown appears, as the name suggests, as a thin covering that is really unsightly. If unchecked this thin film could extend over much of the aquarium décor and smother all underneath.

There is another algae type that often causes alarm and it often appears in a newly set-up aquarium, seemingly – from anecdotal reports – particularly where a decorative sand bed (or possibly a deep sand bed) is in use. It is not a definite appearance however; quite a few aquariums never develop it. It could be a nuisance in older aquariums under certain conditions.

This algae is diatoms. Sometimes they are referred to as brown algae, but this is incorrect, brown algae is another type altogether. The algae could also be mistaken as a form of smear algae as the aquarium décor could be covered with a thin layer. Again, smear algae has nothing to do with diatoms.

Diatom algae rely on silicic acid being present in the seawater. If this remains present in any amount it will be extremely difficult to get rid of the diatoms. Tap water could contain the acid in a sufficient amount to support the algae – if it doesn’t it is likely that it will not appear. If there is a sand bed present maybe silicon is present?*

Wandering off-course for a moment, diatoms have a really wonderful cell structure. I have only seen pictures in books. They could be circular, triangular, oval etc and have intricate patterns within the cell that are individual. I don’t know, but I doubt they are singularly unique, but there are many variations. The cells, which are constructed of silicon, don’t degrade and are in fact used in diatomaceous filters. The media is simply made up of these cells.

Anyway, if the aquarist has an invasion of diatom algae then the first thing to do is wait. After a week or two the diatom problem will often die back and cease to exist. The die back usually is not instantaneous but occurs over a period.

If the problem is getting worse, and/or there isn’t any die back, then it is likely that silicic acid is being supplied. I’m not sure of the sand bed bit, but perhaps silicon content within the sand bed is the culprit. If so, then the silicon should exhaust?* Obviously the aquarist should not be tempted to change the sand bed as this could well make matters worse or extend the period when the diatoms are present.

If the aquarist is using tap water then he or she could have the water tested for silicic acid content. If routine seawater changes are being done, as they should be, and the acid is present in the water then fresh supplies are being provided and the diatoms will not go away.

Another way to deal with the tap water is to use reverse osmosis (RO) water. This is tap water that has been filtered through a very fine filter and much of the unwanted content of the water is removed. The purity of the water when leaving a RO filter is generally from 95 to 98%. The use of RO water is recommended whether there is a diatom algae problem or not. RO filters are available to the hobby commercially, are not particularly expensive, and are a good investment.

So, despite the attractive individual cells of diatom algae, the alga is not wanted. Of the nuisance algae types this is probably the easiest to deal with.

(* I have never seen any ‘official’ or science proven reports about the affect of new sand beds in marine aquaria)