Algae

This is often the first algae to appear in a new tank, where conditions have yet to stabilize. It will often appear rather quickly, within a few months of establishing a tank. When conditions stabilize, it may disappear as quickly as it arrived. It is essential to minimize nutrient levels to ensure the algae disappears; avoid overfeeding and perform weekly maintenance. (water changes, gravel and filter cleaning, etc) This algae can grow in low levels of light and can out compete green algae under these conditions, so, limiting the light will not stop this algae.

If brown algae appears in an established tank, check nitrate and phosphate levels and increased water changes. Using a phosphate-adsorbing resin will also remove silicates, which are important to the growth of brown algae. Because of its ability to grow at low light levels, it may also appear in dimly lit tanks, where old fluorescent bulbs have lost much of their output. Change the fluorescent bulbs if they are somewhat old. If this does not solve your problem, try algae eating catfish like Otos and Siamese algae eaters.

There are many theories as to why this algae often appears in newly set up tanks and then later disappears. If the silicate (Si) to phosphate (P) ratio is high, then diatoms are likely to have a growth advantage over true algae types and Cyanobacteria. Some of the silicate may come from the tap water, but it will also be leached from the glass of a new tank, and potentially from sand/gravel substrates to some extent. Later, when this leaching has slowed, and phosphate is accumulating in the maturing tank, the Si:P ratio will change in favor of phosphate, which is likely to favor the growth of green algae instead.

Blue-green algae/Cyanobacteria

"Blue-green algae" is not actually and algae, rather, a Cyanobacteria. (a group of bacteria capable of photosynthesis) It can appear as a slimy coating in a number of different colors, but mostly a bluish green. "Blue-green algae" can smother plants and may release toxins harmful to fish. It can also fix nitrogen and therefore occur in tanks with zero or very low nitrates. It can be manually removed easily, as it often forms loose sheets, but it's likely to return quickly. Treatment includes improving circulation/aeration in the tank and treatment with erythromycin. (this may however affect the filter bacteria, so it will be necessary to check for ammonia and nitrite after dosing)

Green algae

Green algae can easily occur in tanks with sufficient lighting. Really the only way to remove it is to manually remove it.

Hard algae (a.k.a. green dot algae) appears as small round dots on the aquarium glass. It usually appears to be a normal part of planted tanks with high light levels. Algae-eating fish cannot remove this algae and manual removal requires very hard scraping. Magnetic algae scrapers will not get the job done. My recommendation is to use a Scotch Bright sponge, the one with a course side, and scrub your heart out. Believe me, it is very hard to get off the tank sides. I had it a few years ago on my ten gallon tank which is in my attic now. There is still algae markings on the side of the tank to this day. This is the tank with a white box in it to make it easier to see.

Hair algae occurs as long greenish or gray strands. Some fish, such as Rosy Barbs, will consume it. It can easily be pulled out of the tank.

Red/Brush algae

Brush or red algae can be very difficult to remove manually. It is favored in tanks with a high pH and carbonate hardness. This leads some people to believe that it uses bicarbonates as a carbon source. Limiting phosphate and silicate (by use of RO/DI water or specific adsorption resins) should prevent this algae. Siamese Algae Eaters and common plecos will eat Red algae.

Prevention Tips

Following these tips will help prevent an algae outbreak in your fish tank:

Add powerheads to increase water circulation and create a ripple on the water surface to promote aeration.

Avoid adding Phosphate (in tap water, certain poor carbons, buffer additives and some foods).

Clean filter sponges weekly. Wash sponges in a small bucket of aquarium water or dechlorinated water to prevent tap water chlorine or too high/low temperatures killing off beneficial Biological filter bacteria.

Avoid the use of lamps with a high percentage of red/orange even when growing water plants.

Vacuum/siphon regularly the top layer of sand to remove excess detritus.

Add live plants

When any algae is removed from the aquarium glass by sponging/scrapping, it is recommended to clean the Biological filter sponge after 12-24 hours to remove collected algae. This will prevent Nitrate and Phosphate within the algae breaking down and going back into solution as the algae dies.

Monitor the pH regularly. Adjust with partial water changes and/or Phosphate free buffer additions.

Keep aquarium lights on a timer for 8-10 hours a day.

Feed fish sparingly. Do not allow food to lie uneaten within the tank or Biological filter. All food should be consumed within 1-2 minutes.

Do not overstock the aquarium.

Test kits to measure Nitrate, Phosphate and Ammonia are available commercially. Use when algae appears to help determine its cause.

Ensure that Biological filters are of sufficient capacity to keep Ammonia at undetectable levels as algae will readily feed on Ammonia.