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Mention the word algae to a marine aquarist and the first thought is usually ‘marine nightmare’. Hair algae usually meets this criteria. It is unloved and unwanted. Strange to think that in the very early days of the marine aquarium the aquarist would be pleased to see the algae growth as it would improve the water quality by feeding on nutrients. Under good lighting, the algae also produces a lot of oxygen. That was true and still is, but nowadays all the aquarist wants is rid of it, or at least the excess growth. There are better ways of maintaining water quality.

The hair algae discussed here is also known as filamentous green algae. That is because it grows, if allowed, in large groups with long very thin and flexible ’leaves’. It is a hardy algae and can spread quite alarmingly, causing trouble in a reef aquarium and potentially in a fish only aquarium.

So how can this nuisance algae be controlled. ’Prevention is better than cure’ is a well known saying and without doubt it is applicable here.

This algae requires nutrients to prosper, as do all living things. The major nutrients that concern the aquarist are phosphate (PO4) and nitrate (NO3). A reef aquarium should have a nitrate level of 10 ppm (parts per million) or less, probably best as undetectable. Phosphate should be 0.03 ppm or less, preferably undetectable. The fish only aquarium should have levels as low as possible, though these may be inevitably higher because of a bigger bio-load, that is, more fish.

The obvious first move is to deny the algae the nutrients. It is a very good thing that from the very start the aquarist uses R/O (reverse osmosis) water. This will ensure that the initial fill, routine water changes and make up water are as pure as possible. If the aquarium is already up and running, it is advisable to begin using R/O water for top-ups and routine water changes.

The aquarist may well state with justification that the aquarium filtration employed is live rock, and that will deal with nitrate. Correct, it will, if present in sufficient quantity and quality. However, all things have limits, and over feeding and/or overloading the bio-filtration will result in nutrients.

A major source of nutrients is feeding, particularly with beginners. Feeding the fish is a most enjoyable task, and at the same time the aquarist is concerned that the fish have enough. There is a danger that excess food will enter the seawater and it will not be consumed. It will break down and nitrate will appear. Phosphate also is mainly introduced with food. Prepared marine flakes are not specially processed and do produce nutrients despite the early and incorrect assumptions of some new aquarists. It is clear that feeding should be a disciplined affair, enough being fed but without excess. Fish can consume enough food, but their instinct is to ‘grab it while its there’, and some food can pass through the gut semi digested.

If the aquarist finds that the nitrate and/or phosphate level is higher than desired and has critically examined the feeding discipline, is sure the bio-filtration is not overloaded, and is carrying out routine water changes, then there are further means to assist in dealing with the algae. One or a combination may be effective.

Nutrient Reduction By Filter.

Phosphate can be reduced by using an anti-phosphate resin in a filter, often called a reactor. The phosphate is absorbed and is therefore removed from the seawater. Nitrate can be reduced by use of a filter where certain media is used and kept in a very low oxygen condition. Bacteria extract oxygen from the nitrate and break it down.

Nutrient Reduction By Sump.

A sump can be used to house a deep sand bed (DSB) which will act as a filter, and in addition the macro-algae Caulerpa can be grown in the sump. The Caulerpa will use nitrate and phosphate itself and thus compete with the filamentous algae. When there is sufficient Caulerpa the filamentous algae will be starved of nutrients.

There is another way to deal with the nuisance algae. The nutrient levels should be reduced as far as is possible, but the hardy hairy stuff may persist! If this is the case, then lets use the algae as a food.

Predation By Fish.

The aquarist can introduce certain types of fish to eat the algae. Theoretically, an equilibrium could be obtained, the fish eating the algae, producing nutrients, and the algae re-growing to be eaten again. This is more difficult than it sounds. The aquarist must beware of overloading the bio-filtration and overcrowding the aquarium. Any algae eating fish should be introduced slowly, one at a time, and regard given to their eventual size and compatibility with current livestock. Two types of fish that could be of use are the surgeon fish and rabbit fish families. The latter are generally more hardy.

Predation By Snails, Urchins, and Hermit crabs.

These are very useful in the struggle with nuisance algae. In this topic, the algae is the filamentous type and it is clearly very important to properly research the life forms to ensure that they will in fact eat the algae type. Again, although there is less of a concern with overloading the bio-filtration, introduce them slowly and observe the affect on the algae. More can always be introduced. If too many are introduced initially, then the excess are going to die, definitely not wanted.

So there are ways to battle the nuisance filamentous algae. Nutrient level control is always the first thing to achieve. Then other considerations can be given. The algae seems to be able to hang on despite the loss of food, but it will slowly reduce. If full control cannot be achieved, then using it as a food source for fish etc is another option.

Finally, that requirement of all marine aquarists should be mentioned - patience!