By Donna M. Recktenwalt
Aquarists have long known the value of greenwater.
Basically, it’s green because of the photosynthetic algae and protozoans it contains, such as Euglena. It’s an excellent food for daphnia, but it’s also food for zooplankton such as rotifers, and the larger protozoans such as paramecium, making greenwater an excellent food for fry. “The beauty of greenwater is that it is a sort of balanced ecosystem and you don’t have to worry so much about overfeeding the fry,” says Eric Lund. “In the best setups, greenwater is produced in the fry tank and no feeding is required at all until the fry get large enough to eat baby brine shrimp, at which time they can be dipped from the tank and reared in a grow-out container.”
This contradicts the generally accepted rule of “keep fry in clean water,” but has been proven to work by numerous aquarists. Benefits cited include fewer water changes, faster growth rates resulting from the constant presence of food, and the ongoing “cleanup” activities of microorganisms.
There is no doubt about the benefits of greenwater, but how do you start–and then maintain–a viable culture?Start with Aquarium Water
“The microorganisms that make up greenwater are already in aquaria,” points out Scott Davis, so the basics are simple: well aged tank water, starter, and a source of bright light, either natural or artificial, that is available 14-24 hours a day. Within a few days to a week from the start the water will take on a greenish tinge, and microorganisms will be visible under a microscope. Eventually, given enough light and enough nutrients, the water may turn dark green and become quite opaque.
Remove any plants, which compete with the algae for the available nutrients. Keep the water moving with an airstone or a small box filter filled with stones. Add fish to eat quantities of food, stir up the water, and produce waste material. “Under optimum conditions greenwater reproduces at an incredible rate,” with 40% removal possible every few days.
There are a number of “recipes” for making greenwater. Dave Lains uses a small but effective system: one goldfish, one gallon bowl, leftover brine shrimp, and lots of light.
Or try this one from Mack Fukada: to tank water, add a crushed (or microwaved) lettuce leaf and some liquid plant nutrient, such as Miracle Grow fertilizer. (Many aquarists with plant tanks have found that fertilizers result in unusually high nitrate and phosphate levels, which result in unwanted algae blooms; for greenwater production, this situation is ideal and poses no problems to fish or snails.)
Dave Webb, too, begins with Miracle Grow fertilizer, then adds iron drops such as Sequestrene (available at garden stores) or Duplaplant 24. “If you let the iron levels drop,” he says, “the water may not stay green.”
Others, like Dale Deck, use water left over from boiling potatoes, placed near a sunny window. To feed the culture, add more potato water or cooking water from any starchy cereal grain. Alternatively, use a bit of liquid or powdered milk. These cultures are not odorless, but do produce a culture quickly.
If you feel adventuresome, you might try this recipe from Scott Page. In a blender place 2 cups of RO/DI water and one sheet of Nori (dried algae, for wrapping sushi; available in red, brown, and green). Liquify for 5 min. Filter first through window screening sized mesh, then through the finest mesh you can find. The resulting liquid will feed rotifers or baby brine shrimp. The remaining jelly can be used fresh or frozen as food for small-mouthed herbivores, daphnia, brine shrimp, etc.
– G.C.K.A. Newsletter, April 1999