Sooner or later most hobbyists encounter a green tank. Usually this occurs early on in the hobby, and we learn quickly certain things that will help us prevent the problem along the way, but occasionally we still have the "pea soup syndrome" occur for no apparent reason. For the purposes intended by this article, we will touch on some of the reasons this occurs and how to combat it.
All too often we are tempted to set a tank up in a place that seems esthetically wonderful. Too often this means in front of that beautiful bay window, or in the sunroom, or in a very well lit area within the house. What we do not realize is that the very fact that the tank is exposed to sunlight is a major cause of green water. Another leading cause is the use of the tank as a night light, or simply sometimes lacking the initiative to turn the lights off at night. No matter what the situation, the fact that the tank is exposed to excessive light is almost always the direct cause of green water.
Now before we simplify this too far, there are other causes as well. High levels of Nitrate or Phosphates can certainly contribute to this, and often are found in tanks that are green as well, but the trigger almost invariably is light.
So how can we combat this condition. Anyone experiencing this knows all too well that simply changing water does little to alleviate the condition, and by simply removing or reducing the light source is little more effective, since the problem continues to reoccur even after the light has been eliminated as an ongoing contributor. But to understand this better, we need to discover exactly what green water really is.
We assume that green water is algae floating in the water. This is not entirely true. While algae is a contributing factor, what you actually see is free floating bacteria, not exactly the same as the nitrifying bacteria that help keep our tanks healthy, but very closely aligned. These bacteria form opportunistically, feeding on organic material that is present in the tank, in this case on algae cells as they first form. Since they feed on this algae, the bacteria take on the color of the diet that sustains them. This is similar to the color exhibited by anemones in marine environments. In anemones, this symbiotic relationship is welcome, in fact sought after.But in the case of the average aquarium, especially freshwater, this is not. But once this condition arises, there are steps that will help relieve and eliminate it's ongoing existence.
First, we need to eliminate the light source. Not completely mind you, since we like illuminated tanks for the pleasure of our own eyes. When we are not around, keeping overhead lights on for shorter periods of time certainly is a viable option. Blocking natural sunlight is essential. Sunlight feeds the developing algae faster than any artificial light source. Blocking the incoming sunlight is critical if the green water is to be eliminated. Sometimes this means moving the aquarium to another site, sometimes a background or drawing the shades will accomplish the needed light blockage. Either way, only when the sunlight is eliminated do we stand a chance of defeating the problem.
Next we need to find possible nutrient sources. Check the water for the presence of excessive nitrates. Generally these are kept in check by regular water changes and effective cleaning of the gravel bed. Never completely clean the bed, or the resulting bacterial bloom will be as irritating and discouraging as the initial problem. If Nitrates are high, a series of water changes will help to bring them down, although don't change too much too fast, because invariable a tank with high nitrates means that either it has been fed heavily, or has been ignored for a while, and this can also mean great differences in pH and such between the old water and the new, and the sudden change can be hazardous if not fatal to the inhabitants of the tank.
Also a distinct possibility when encountering green water is the presence of phosphates. Phosphates can gain entry to the tank in a number of ways. Often it is present in tap water, and simply changing the water can actually make the situation worse. If this is the case, then consideration must be made to deal with the phosphates. Using resins to absorb the phosphates is one option, using water that contains none is another. The latter can be obtained from a number of sources, including reverse osmosis water, distilled water is another. Using systems such as Aquarium Pharmaceuticals Tap Water Purifier will also eliminate the presence in your tap water.
A second possible source of phosphates is from products we use in our aquariums. Many plant foods contain phosphates, although usage of live plants will usually help keep green water from occurring. A less obvious source of phosphates is in many water conditioners, especially the thicker "slime coat enhancers" that are promoted heavily in the hobby. Often discontinuing their usage will help eliminate runaway phosphates. Even less obvious is the water that is used to pack frozen foods. Often this water contains phosphates, and if the food is not rinsed well before feeding, these phosphates are passed into the tank.
Once the potential causes have been recognized and remedied, treating the green water is fairly easy. Water changes will eliminate the color and overpopulation of bacteria, or if you own a powerfilter, which most of us do now, you can use a most unique product to remove the excess green bacteria overnight. This product is called Filter-Aid from Aquarium Products. Many Local Fish Shops do not carry this product, but most can get it, they are simply unaware of it's value. More on this product can be obtained in our current product review section.
Once the water has returned to it's clear and pleasant form, simply keep lighting down to a minimum, keep nitrates and phosphates down, and keep up on the regular water changes and it should not return.