Biofilm is an integral part of every aquarium ecosystem. It develops as a slimy layer that covers rocks, wood, plants, leaves, seed pods, substrate, glass, and other submerged surfaces within the tank. The key components of biofilm include microorganisms, extracellular polymeric substances, and organic matter. Sometimes appearing whitish or brown, it's more often imperceptible to the naked eye, yet serves as a natural, nutritious food source for aquarium inhabitants such as fish, shrimp, and snails. Biofilm is usually a sign that things are working right in an aquarium, a tangible indicator that natural processes (usually unseen) are at work.
Biofilm forms when microorganisms (mostly bacteria but also fungi, algae, diatoms, and protozoa) colonize underwater surfaces
- The microorganisms excrete a slimy, glue-like substance, consisting of extracellular polymeric substances including polysaccharides, proteins, and lipids
- That slimy substance protects the microorganisms and allows them to adhere to surfaces
- Organic matter such as decomposing plant detritus, fish waste, and uneaten food also becomes entrapped in the biofilm matrix
The development of biofilm starts with a few bacteria and other microorganisms taking advantage of the abundant surface areas that an aquarium aquascape offers
- The early adapters put out the welcome mat for other microorganisms by providing more diverse adhesion sites, ei., the matrix of sugars that holds the biofilm together
- Since some microorganism species are incapable of attaching to a surface on their own, they often anchor themselves to the matrix or
directly to their friends who engendered the colony
Biofilm first appears in new tanks when the nitrogen cycle begins
- It can be mostly imperceptible, but it can also take on a white, fuzzy appearance, often feeding on sugars and cellulose leaching from new driftwood or botanicals (eg., leaves or seed pods)
- Nutrient surplus, from excess food or waste, also fuels biofilm development, causing it to appear on substrates, rocks, and other
submerged surfaces
Benefits of biofilm for the aquarium ecosystem
- Vital food source for snails, shrimp, and some fish
- Key to the biological water filtration that nitrifying bacteria provide, driving the nitrogen cycle
Potential downside of biofilm
- Excessive buildup of surface biofilm can hinder gas exchange with the atmosphere
- Hindered gas exchange can lead to lower oxygen levels that can put undue stress on all aerobic aquatic inhabitants, including fish, shrimp, snails, microbes, and even plants
- Surface biofilm often looks like an oily or greasy slick on the water's surface
- Frequently caused by bacteria feeding on high levels of proteins and fats from fish food or waste
- This condition is exacerbated when surface agitation is low
- Surface biofilm often develops in the presence of aquarium CO2 injection for the benefit of plants
- Injecting CO2 does not directly create surface biofilm, but it often causes it indirectly
- Increased nutrient uptake by rapidly growing plants, coupled with reduced surface agitation (usually minimized intentionally by aquarists to prevent CO2 loss), allows organic compounds and bacterial colonies to accumulate, resulting in an oily surface film
- Surface biofilm can be removed to restore free gas exchange, three helpful methods can be employed
- First, use a surface skimmer
- Second, do it manually with paper towels
- Third, increase surface agitation at night via aeration to help dissolve the film and balance oxygen levels in the water column
Placing botanicals (leaves or seed pods) in an aquarium can greatly increase biofilm formation
- Desirable because certain aquatic inhabitants (eg., shrimp) require biofilm for food
- Freshly added botanicals offer a motherlode of organic material for biofilm development
- For shrimp keepers, biofilm is actively fostered, recognizing the value of having a periodic biofilm crop for shrimp to graze on
- Danger of excess biofilm development in rare instances
- For example, a large influx of fresh botanicals can cause a rapid multiplication of the bacteria within the existing biofilm
- When that large influx comes to an aquarium with a large bioload, the oxygen level in the water can be reduced dangerously low
- In turn that can lead to a dramatic reduction of CO2 being released out of the water
- That, in turn, can lead to CO2 levels rising sharply, causing asphyxiation to the animals in the tank, including the nitrifying bacteria that support it
- Still, a mild bumper crop of biofilm resulting from a modest addition of botanicals is usually very beneficial for shrimp, snails and some fish
- If the burst of new biofilm seems alarming, remember that it's typically a passing phase that can take a few days to a couple of weeks before it subsides on its own to a manageable level
- However, bumper biofilm crops that stem from added botanicals can sometimes seem out of control
- In that case, there are time-tested options to pursue, short of rejecting the whole idea of adding botanicals to the ecosystem
- First, do nothing except appreciate the wonder of nature, no matter how unsightly it may seem temporarily. Allow the shrimp, who adore the stuff, to enjoy the feast
- Second, the offending botanicals can be removed, given a good scrub with a soft bristle brush (like an old toothbrush), rinsed in fresh (dechlorinated) water, and put back
- Remember that in a well-managed aquarium, at best the largest blooms of biofilm will be a temporary nuisance, subsiding to a
tolerable level, or even being almost unseen, for the life of the aquarium
In summary, biofilms are common in nature and part of any aquarium ecosystem
- Nevetheless, they are more significant (and noticeable) when aquatic botanicals are added for the benefit of shrimp or crustacean keeping
- Biofilms are not to be feared, but they should be respected and, ultimately, allowed to support the biological filtration of the water column and to serve as nutritious food for aquatic livestock