Algae Problems

Under certain conditions a bloom of excessive algae growth may develop. Algae usually grow in a fish-only tank because it has no competition. Maintaining a regular routine of partial water changes, thus providing stable, appropriate conditions, deters most algae growth. Various fish and invertebrates can be added to control algae, but their efforts will not amount to much under poor water conditions; algae will grow faster than the fish can feed.

In a minireef, insufficient lighting is likely to favor less desirable kinds of algae. Usually, insufficiency results from aging lamps. Changing them solves the problem, although established algae may require physical removal. A sudden shift in the tank's "algae profile" should alert you to a potential lighting problem. If seaweeds and a sparse coating of bright green filamentous algae abruptly begin yielding territory to reddish purple slime algae or yellowish brown diatoms, check the lighting.

Excess phosphate and/or other nutrients may be fueling rampant algae growth. Purification of the tap water used for making synthetic seawater has helped many an aquarist reduce or eliminate problems.

Many utilitarian invertebrates, and, to a lesser extent, herbivorous fishes, provide a natural check on algae growth.

As with many aquarium situations, preventing undesirable algae from gaining a foothold proves easier than eliminating a bloom. Nevertheless, if you are faced with an overgrown tank, here are some steps you can take:

• Install a reverse osmosis unit to purify your tap water.

• Check to see if your seawater mix or any additive you are using contains phosphate. If so, switch brands.

• Add algae consumers such as snails, sea urchins, or herbivorous fishes.

• Physically remove as much algae as possible on a regular basis.

• Carry out more frequent partial water changes.

• Test your tank for phosphate regularly. As long as phosphate remains detectable, you will have algae.


Being dynamic living systems, saltwater aquariums sometimes unexpectedly develop problems despite our best efforts. Knowing the signs of disease in fish or invertebrates and having knowledge of appropriate remedies allows you to take action before problems become too severe to correct. You will note, however, that the best insurance against trouble comes from maintaining the aquarium properly on a regular basis. Partial water changes, vacuuming debris from the substrate, cleaning algae from the glass, and keeping the lighting at the proper intensity all contribute to a healthy, trouble-free aquarium.

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