I Didn’t Want Any Algae – Not The Nasty Stuff Anyway


The marine aquarist builds and stocks the aquarium to produce a beautiful and absorbing picture, lovely fish gliding among wonderful corals. It seems simple enough.

After a while when the aquarium is well established, stable and particularly where live rock has been used algae appear. This is hopefully decorative and desirable, of various colours and shapes. The leaves themselves can be interesting, some soft and small and others large and rigid. It all adds to the overall picture.

Why does algae appear that is not desirable when all the equipment was carefully chosen?

The basic answer is food. All living things require food and if it is not available or is insufficient the life form will not survive or even appear. Algae, particularly the undesirable stuff, requires nitrate and (maybe ‘or’?) phosphate – if this is sufficient then the yukky stuff will prosper. It usually takes the form of long stringy or bushy green clumps that attach everywhere and/or dark blue green mats that spread over nearly everything. The latter is often referred to as slime algae.

So food has been mentioned. Removing the food should remove the algae. This is correct though the algae, particularly the hairy green stuff seems to be particularly resistant and hangs on a while. It has to give up eventually though.

First, two test kits should be used to determine the level of food, a better word is nutrients, in the seawater. The two tests are nitrate and phosphate. Some just use the nitrate test and, if overfeeding is avoided, phosphate hopefully will not be a problem. If problem algae is present then it is likely that the test reading will be high. The guidelines suggest nitrate should be less than 10ppm (parts per million) for a reef system and less than 30ppm for a fish only system. Phosphate should be hopefully shown as zero on the test, or not more than 0.03. The levels should always be as low as possible.

So how is the nutrient supply controlled? First checks need to be made. Is the aquarium overstocked with fish? If there are too many fish for the seawater gallonage then fish wastes along with the necessary fish feeding are not going to be helpful. Overstocking must be avoided. Feeding the fish is pleasurable, but excess feeding must be avoided – when the fish start to lose interest, stop feeding. Unused fish food adds nitrate and phosphate to the seawater. Additionally there is the practice of routine seawater changes – in this case the guideline suggests 10% of the net gallonage (including sump) of the system per week. The amount of seawater change can be increased to speed the arrival of good nutrient free seawater but should never exceed about 25% of the net total volume except in an emergency. Excessive ‘raw’ new seawater can sometimes have an adverse effect on corals and sensitive fish.

When preparing seawater for a routine change it’s worth considering using reverse osmosis (RO) water. RO water is produced by running tapwater through carbon and then a very fine filter. Pollutants are nearly all removed and the water is as clean as possible, usually 95 to 98% pure. Using RO water for evaporation top-ups is also worthwhile. RO units are not particularly expensive and can be purchased in various ‘gallons per day’ sizes so that demand can be matched.

Once stocking, seawater changing and feeding are considered acceptable then the aquarists’ watchword ‘patience’ comes into play. Clumpy and stringy green algae can be removed to an extent by wrapping it round a stick by twisting but care needs to be taken that damage to the reef structure is not caused. This practice needs to continue until there is no more removal possible. Smear algae does not like excessive seawater movement so it follows that seawater movement needs to be checked and increased if found insufficient. The guidelines suggest 10 times per hour the net volume of seawater (excluding sump) for a fish only or soft coral system, and at least 20 times per hour for a reef of hard corals. If smear algae seems to be mostly in one area then seawater movement could be increased to that area by the careful adjustment of powerheads, always being careful not to directly point a powerhead at corals. When partial seawater changes are being done then some of the smear algae could hopefully be siphoned out and disposed of.

Some of the algae that is present could well become loose and float about or lay on the bottom. As this algae rots it releases nutrients back into the seawater so it should be siphoned out and disposed of.

Another item to check is lighting. Lighting should be regularly changed, be it fluorescent or metal halide. The manufacturer’s recommendations should always be noted, but generally one year is enough for a tube or bulb. Particularly with tubes, changes are required because of power loss (meaning less light penetration) and spectrum shift. Corals in particular require a certain spectrum of light to prosper, as the tubes/bulbs age the spectrum alters and this starts to be lost. Tubes could begin to emit more light in the ‘red’ area which would be of benefit to problem algae.

Consideration should also be given to the amount of time the lighting is on. Generally, the lighting seems to be on between 8 and 12 hours a day with marine aquarists, particularly those with a reef system. The lighting time should be minimised to the time that equates with healthy corals. Having lights on say 15 or more hours so that the aquarium can be viewed for longer is not good. It’s better to alter the lighting timing so that the aquarium is viewable without excess lighting hours.

Though there will be a protein skimmer in operation (there should be!) double check that it is adequate for the amount of seawater it has to deal with. The skimmer should be regularly checked and cleaned of the brown scum that collects particularly in the throat. An adequate and correctly functioning skimmer removes much of the disolved organics in the seawater.

There are methods of combating excessive nutrients in seawater using apparatus or using algae itself in a controlled environment. However it is far better to control the nutrients by good management practices.

So the battle against unwanted algae is a question of management. If the areas suggested are targeted then in time the algae will surrender. ‘In time’ is important because nuisance algae will not go away overnight – the aquarist needs to give time in the battle and be patient.

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  1. Once I had huge menace of this unwanted algae. I checked and altered everything but failed. Then only I tried to adjust lights and after that me and fishes were both happy.

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