Algae out-breaks are common in African Cichlid aquariums. In this article, I will explain why, and also give some pointers on how to rid your tank of it and prevent its return.
Algae is a plant, and plants need four things to grow: light, nitrogen, phosphate, and potassium. Let's take a look at these in order.
Fortunately, cichlids donít have any specific wavelength requirements. Plants, on the other hand, predominantly use blue and red light, while reflecting green. (Lamps that emit red and blue light shed a fluorescent purple light on your tank.) Now cool white and a lot of cheap aquarium tubes are heavy in the yellow/green spectrum, which just so happens to be what we see best. By using one of these lamps, you deprive algae (and other plants) the wavelengths they need most. Donít get too excited, however, because algae will readily adapt to any environment, but by using a lamp heavy in yellow and green light, you are putting the algae at a disadvantage.
One of the greatest causes of algae out-breaks can be linked to running the lights too long. With my first tank, I used to run my light (which unfortunately came from a reef tank, and emitted red and blue light) 16 hours a day. As a consequence, I couldn't ever keep my water clear. Cichlids donít need lots of light, nor do they need any specific wavelength. A good rule of thumb is to not run your lights for more than 10 hours, and certainly not more than 12. Also, whenever possible, keep your tank out of direct contact with sunlight. Sunlight will only turn your water green before you know what happened, not to mention the drastic temperature fluctuations it will inflict upon your fish.
Plants need nitrogen in order to grow. They get this from your fish. Most of the nitrogen in a tank actually comes from fishes' gills, but a large percentage also comes from fecal waste. I won't go into any detail about the nitrogen cycle here, but once nitrogen has been broken down into NO3, it can be used by plants, such as algae. Overstocking your tank or overfeeding the fish can cause nitrate levels to skyrocket--providing an environment for algae to flourish and a stressful environment for your fish.
Regular water changes, proper and sufficient filtering, and even cichlid-friendly plants (e.g., Anubias spp.) will ensure that nitrate levels stay where they should be--below 25ppm.
Perhaps the number one reason for algae outbreaks in Cichlid tanks is due to the water requirements of these fish. Cichlids require "hard" water, with lots of minerals. Magnessium, Bicarbonate, and Phosphates are among the most common minerals in tap water. Plus, a lot of commercial fish foods have Phosphate added to them. There is not much you can, or should do, to lower the phosphate levels in an African Rift Lake aquarium.
There is not a whole lot to say about this. Potassium is found in many fertilizers, and you only have to watch out for this if you are trying to grow other plants. But, Potassium can actually be beneficial in helping other plants to uptake other nutrients. These other plants can then (hopefully) outcompete the algae.
There are a lot of chemicals out there that claim to kill the algae and return your tank to its previous clarity. With my first tank, I tried "Algae Destroyer," and "Brite N' Clear." They did work, but they also killed off my plants. I would discourage you from using these regularly becuase they chelate (i.e., remove) excess phosphates from your water, which is needed to maintain the water conditions your cichlids prefer.