Water garden slime is more commonly referred to as green water algae and is nothing more than the very natural oxygenating organism called cyanobacteria.
Blue-green algae or brown or black, are all forms of cyanobacteria or what both the uninformed and common Joe alike, refer to as slime or smear algae.
Cyanobacteria is carried on the wind, and is natures way of oxygenizing anaerobic conditions in water, especially wherever high levels of organic wastes and nutrients have been dissolved.
As cyanobacteria is a very simple organism, it uses only photosynthesis to reproduce, and will easily inhabit any imaginable aquatic location be it, saltwater, freshwater, rock or even soil.
Some animals also use algae to their benefit either to produce energy or protect themselves in some way, such as a few endosymbiont species in protests, lichens or the sloth for example that grows cyanobacteria in its fur as a kind of camouflage.
Cyanobacteria can be unicellular or colonial and colonies form in three types, filaments, and sheets or hallow balls. Filamentous colonies can be vegetative, akinetes or heterocysts.
Heterocysts are thick-walled and contain enzyme nitrogenase, vital for nitrogen fixation and can fix nitrogen gas that cannot be used by plants, into ammonia (NH3), nitrates (NO2-) or nitrates (NO3-) which can be absorbed by plants and converted into protein and nucleic acids.
So why is such a useful oxygenator as aquarium slime or watergarden slime taken as dangerous or offensive to the delicate artificial environments?
Basically, aesthetics, but if given enough sunlight, algae can takeover, and throw the whole environment out of balance.
In a worse case scenario, some particular species of cyanobacteria can produce neurotoxins, cytotoxins, hepatotoxins and endotoxins, making them dangerous for mammals and other animals, including us humans (not a good idea to drink algae water without testing).
Although our species still has yet to understand cyanobacteria completely (preventing us from accurately assessing risks) according to some sources (see links below) several cases of human poisoning have been documented from either drinking water or recreational pond water.
In the case of aquarium algae, depending on if the aquarium is saltwater or freshwater, usually merely a change of the water or a partial change of the water is in order, but as saltwater aquariums are difficult to clean out, the best things are slime sumps.
Thriving slime slumps can even be a ready solution to freshwater aquarium slime as well as saltwater aquarium slime, but rerouting that kind of water to a biological filter filled with bioballs and other slime forming surfaces, just may not be the kind of energy efficient solution most freshwater aquarists are looking for (unless they have sustainable energy sources like a solar pump).
Watergarden slime is just as necessary as aquarium slime, but in a watergarden, algae is a must, especially when there is a serious lack of oxygenation.
60% of the oxygen produced in ponds is from cyanobacteria alone.
In Asian rice patty fields, where 75% of the worlds population gets its food, healthy nitrogen-fixing cyanobacteria populations keep the balance in paddy waters to produce year after year.
Cyanobacteria is important to keep the whole biological ecosystem thriving in a pond or watergarden as it eliminates bad news gases that plants cannot digest well.
Chemical removal is possible, but will eliminate all bacteria in the water and should be used sparingly, 200mg of erythromycin phosphate per 10 gallons of water should do it, but not recommended before physical scraping and cleansing of all rock, glass, gravel and plastic plant/ornaments have been done, including vacuuming substrate.
Regular cleaning and regular water changes are sure to keep green slime away the best, much better than chemical removal, but once again, in the cases of watergarden slime and saltwater aquarium slime, regular removal is not an option due to the time necessary to balance the aquatic environment, so best to do it correctly only once (before building any delicate environments).
In any closed aquatic environment, cyanobacteria; aquarium slime or watergarden slime is sure to be found, especially if fish and plants are present and the dirtier the water and the more sun, the more green water algae can bloom.
Water garden slime is a natural gas processing organism that breaths life intoNeptunes most sacred sanctums; these temples of underwater splendor.
Cyanobacteria, their toxins and health risks.