Beneficial Bacteria

[D24]

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Nitrifying Bacteria Facts by Fritz Industries

One of the most important, and least understood, aspects of successful aquarium keeping is biological filtration and its function in the nitrogen cycle. Traditionally, novice aquarists become disillusioned at the frequently experienced high death rates of their aquatic pets after setting up a new aquarium. Statistically, as much as 60% of the fish sold for a new aquarium will die within the first 30 days. 2 out of every 3 new aquarists abandon the hobby within the first year.

Known as "New Tank Syndrome" these fish are poisoned by high levels of ammonia (NH3) that is produced by the bacterial mineralization of fish wastes, excess food, and the decomposition of animal and plant tissues. Additional ammonia is excreted directly into the water by the fish themselves. The effects of ammonia poisoning in fish are well documented. These effects include: extensive damage to tissues, especially the gills and kidney; physiological imbalances; impaired growth; decreased resistance to disease, and; death.

Nitrite poisoning inhibits the uptake of oxygen by red blood cells. Known as brown blood disease, or methemoglobinemia, the hemoglobin in red blood cells is converted to methemoglobin. This problem is much more severe in fresh water fish than in marine organisms. The presence of chloride ions (CL-) appears to inhibit the accumulation of nitrite in the blood stream.

The successful aquarist realizes the importance of establishing the nitrogen cycle quickly and with minimal stress on the aquarium’s inhabitants. Aquarium filtration has advanced from the old box filters filled with charcoal and glass wool to undergravel filters, then trickle filters, and most recently - fluidized bed filters. Every advance has been to improve upon the effectiveness of biological filtration which in turn increases the efficiency of the nitrogen cycle. The availability of advanced high-tech filtration systems has lent added importance to the understanding of basic aquatic chemistry.

Nitrifying bacteria are classified as obligate chemolithotrophs. This simply means that they must use inorganic salts as an energy source and generally cannot utilize organic materials. They must oxidize ammonia and nitrites for their energy needs and fix inorganic carbon dioxide (CO2) to fulfill their carbon requirements. They are largely non-motile and must colonize a surface (gravel, sand, synthetic biomedia, etc.) for optimum growth. They secrete a sticky slime matrix which they use to attach themselves.

Species of Nitrosomonas and Nitrobacter are gram negative, mostly rod-shaped, microbes ranging between 0.6-4.0 microns in length. They are obligate aerobes and cannot multiply or convert ammonia or nitrites in the absence of oxygen.

Nitrifying bacteria have long generation times due to the low energy yield from their oxidation reactions. Since little energy is produced from these reactions they have evolved to become extremely efficient at converting ammonia and nitrite. Scientific studies have shown that Nitrosomonas bacterium are so efficient that a single cell can convert ammonia at a rate that would require up to one million heterotrophs to accomplish. Most of their energy production (80%) is devoted to fixing CO2via the Calvin cycle and little energy remains for growth and reproduction. As a consequence, they have a very slow reproductive rate.

Nitrifying bacteria reproduce by binary division. Under optimal conditions, Nitrosomonas may double every 7 hours and Nitrobacter every 13 hours. More realistically, they will double every 15-20 hours. This is an extremely long time considering that heterotrophic bacteria can double in as short a time as 20 minutes. In the time that it takes a single Nitrosomonas cell to double in population, a single E. Coli bacterium would have produced a population exceeding 35 trillion cells.

None of the Nitrobacteraceae are able to form spores. They have a complex cytomembrane (cell wall) that is surrounded by a slime matrix. All species have limited tolerance ranges and are individually sensitive to pH, dissolved oxygen levels, salt, temperature, and inhibitory chemicals. Unlike species of heterotrophic bacteria, they cannot survive any drying process without killing the organism. In water, they can survive short periods of adverse conditions by utilizing stored materials within the cell. When these materials are depleted, the bacteria die.


Biological Data
There are several species of Nitrosomonas and Nitrobacter bacteria and many strains among those species. Most of this information can be applied to species of Nitrosomonas and Nitrobacter in general., however, each strain may have specific tolerances to environmental factors and nutriment preferences not shared by other, very closely related, strains. The information presented here applies specifically to those strains being cultivated by Fritz Industries, Inc.


Temperature
The temperature for optimum growth of nitrifying bacteria is between 25C-30C.

Growth rate is decreased by 50% at 18C.
Growth rate is decreased by 75% at 7C-10C.
No activity will occur at 4C
Nitrifying bacteria will die at zeroC.
Nitrifying bacteria will die at 49C

Nitrobacter is less tolerant of low temperatures than Nitrosomonas. In cold water systems, care must be taken to monitor the accumulation of nitrites.


pH
The optimum pH range for Nitrosomonas is between 7.8-8.0.

The optimum pH range for Nitrobacter is between 7.3-7.5

Nitrobacter will grow more slowly at the high pH levels typical of marine aquaria and preferred by African Rift Lake Cichlids. Initial high nitrite concentrations may exist. At pH levels below 7.0, Nitrosomonas will grow more slowly and increases in ammonia may become evident. Nitrosomonas growth is inhibited at a pH of 6.5. All nitrification is inhibited if the pH drops to 6.0 or less. Care must be taken to monitor ammonia if the pH begins to drop close to 6.5. At this pH almost all of the ammonia present in the water will be in the mildly toxic, ionized NH3+ state.


Dissolved Oxygen
Maximum nitrification rates will exist if dissolved oxygen (DO) levels exceed 80% saturation. Nitrification will not occur if DO concentrations drop to 2.0 mg/l (ppm) or less. Nitrobacter is more strongly affected by low DO than NITROSOMONAS.


Salinity
The nitrifying bacteria in Fritz-Zyme #7 will grow in salinities ranging between 0 to 6 ppt (parts per thousand) (specific gravity between 1.0000-1.0038).

The nitrifying bacteria in Fritz-Zyme #9 will grow in salinities ranging from 6 up to 44 ppt. (specific gravity between 1.0038-1.0329).

Adaptation to different salinities may involve a lag time of 1-3 days before exponential growth begins.


Micronutrients
All species of nitrifying bacteria require a number of micronutrients. Most important among these is the need for phosphorus for ATP (Adenosine Tri-Phosphate) production. The conversion of ATP provides energy for cellular functions. Phosphorus is normally available to cells in the form of phosphates (PO4). Nitrobacter, especially, is unable to oxidize nitrite to nitrate in the absence of phosphates.

Sufficient phosphates are normally present in regular drinking water. During certain periods of the year, the amount of phosphates may be very low. A phenomenon known as "Phosphate Block" may occur. If all the above described parameters are within the optimum ranges for the bacteria and nitrite levels continue to escalate without production of nitrate, then phosphate block may be occurring. In recent years, with the advent of phosphate-free synthetic sea salt mixes, this problem has become prevalent among marine aquarists when establishing a new tank.

Fortunately, phosphate block is easy to remedy. A source of phosphate needs to be added to the aquarium. Phosphoric Acid is recommended as being simplest to use and dose, however, either mono-sodium phosphate or di-sodium phosphate may be substituted. Fritz PH LOWER contains 31% phosphoric acid. A one time application of 1 drop per 4 gallons of water is all that is necessary to activate the Nitrobacter. This small dosage of PH LOWER will not affect the pH or alkalinity of marine aquaria.

Minimal levels of other essential micronutrients is often not a problem as they are available in our drinking water supplies. The increasing popularity of high-tech water filters for deionizing, distilling, and reverse osmosis (hyper-filtration) produce water that is stripped of these nutrients. While these filters are generally excellent for producing high purity water, this water will also be inhibitory to nitrifying bacteria. The serious aquarist must replenish the basic salts necessary to the survival of the aquarium’s inhabitants. These salts, however, usually lack these critical micronutrients.


Nutriment
All species of Nitrosomonas use ammonia (NH3) as an energy source during its conversion to nitrite (NO2). Ammonia is first converted (hydrolyzed) to an amine (NH2) compound then oxidized to nitrite. This conversion process allows Nitrosomonas to utilize a few simple amine compounds such as those formed by the conversion of ammonia by chemical ammonia removers.

A few strains of Nitrosomonas are also capable of utilizing urea as an energy source. The strains cultivated for Fritz-Zyme #7 and Fritz-Zyme #9 are among the few that can effectively convert urea.

All species of Nitrobacter use nitrites for their energy source in oxidizing them to nitrate (NO3).


Color and Smell
The cells of nitrifying bacteria are reddish (Nitrosomonas) to brownish (Nitrobacter) in color. The solutions in bottles of Fritz-Zyme #7 and #9 are normally peach to rosy colored due to the natural colors of the bacterial cells and the proprietary solution used to keep them alive. What you see are actually clumps of bacteria stuck together by their own slime matrix.

Solutions of Fritz-Zyme normally have a musty stagnant water smell.

Sometimes the solution may turn dark brown or black and smell like rotten eggs. This is rare but not unusual. This is due to the presence of residual sulfates that have been reduced to sulfides. This has no relationship to the viability of the bacteria. The concentration of sulfides is only a few parts per billion (ppb) and is not toxic when diluted in the aquarium. These sulfides can be degassed before use if preferred by removing the bottle cap and allowing oxygen to go into solution. This can be speeded up by gently aerating the solution for several minutes. The solution will return to its original color. The dark color and bad odor do not indicate whether or not the product has spoiled.


Light
Nitrifying bacteria are photosensitive, especially to blue and ultraviolet light. After they have colonized a surface this light poses no problem. During the first 3 or 4 days many of the cells may be suspended in the water column. Specialized bulbs in reef aquaria that emit UV or near UV light should remain off during this time. Regular aquarium lighting has no appreciable negative effect.


Chlorine and Chloramines
Before adding bacteria or fish to any aquarium or system, all chlorine must be completely neutralized. Residual chlorine or chloramines will kill Fritz-Zyme bacteria and fish.

Most US cities now treat their drinking water with chloramines. Chloramines are more stable than chlorine. It is advisable to test for chlorine with an inexpensive test kit. If you are unsure whether your water has been treated with chloramine, test for ammonia after neutralizing the chlorine. You can also call your local water treatment facility.

The type of chloramines formed is dependent on pH. Most of it exists as either monochloramine (NH2Cl) or dichloramine (NHCl2). They are made by adding ammonia to chlorinated water. Commercial chlorine reducing chemicals, such as sodium thiosulfate (Na2S2O2) break the chlorine:ammonia bond. Chlorine (Cl) is reduced to harmless chloride (Cl- ) ion. Since dichloramine has two chlorine molecules, a double dose of a chlorine remover, such as sodium thiosulfate, is recommended.

Each molecule of chloramine that is reduced will produce one molecule of ammonia. If the chloramine concentration is 2 ppm then your aquarium or system will start out with 2 ppm of ammonia. Chlorine Remover will reduce up to 2 ppm of chlorine at recommended dosages. During the warmer months chlorine levels may exceed 2 ppm. A double dose would be required to effectively eliminate the excess chlorine.


Adding Bacteria
After all the chlorine has been safely neutralized Fritz-Zyme should be added to rid the aquarium of ammonia. Depending on the aquarium pH, 3-4 days may be advisable before adding your fish in order to minimize stress. If the water supply does not contain chloramines, and there is no ammonia, Fritz-Zyme should be added at the same time as the fish.












Fritz-Zyme #7 (for fresh water) and Fritz-Zyme #9 (for salt water) Biological Water Conditioners are the sure, safe answer to rapidly establishing the nitrogen cycle within any closed aquatic system. They are the only concentrated cultures of active autotrophic nitrifying bacteria available and should not be confused with the many products that are comprised primarily of different species of heterotrophic bacteria (see our technical bulletin: Nitrifying Bacteria Facts - Autotrophs vs. Heterotrophs).

Fritz-Zyme #7 & Fritz-Zyme #9 contain strains of Nitrosomonas and Nitrobacter species bacteria of the family NITROBACTERACEAE - the true nitrifiers. Five genera are generally accepted as ammonia-oxidizers and four genera as nitrite-oxidizers. Of these, Nitrosomonas (ammonia-oxidizers) and Nitrobacter (nitrite-oxidizers) are the most important. Marine species are different from those that prefer fresh water, and yet, are very closely related. Each species has a limited optimum range for survival. They are the most efficient, and most important, group of nitrifying bacteria and are ubiquitous (world-wide) in their distribution.

Fritz Industries pioneered a revolutionary process that decreases their metabolic activity to allow these bacteria to remain viable for six months in their package. Laboratory tests have shown that attempts by other competitors to package nitrifying bacteria with extended shelf lives have failed to produce viable bacteria, and especially, viable Nitrobacter.

[.Hack]

Great info there bro!

[D24]

Biological Science Department, California State University. Released by Fritz Industries, Inc.


FritzZyme™ was scientifically proven to be the absolute best source of nitrifying bacteria available, as shown in a independent study performed at the Biological Science Department at California State University. The large project was directed by experts in aquatic nitrification. When contacted by these biologists for samples, Fritz Pet Products was eager to have their bacteria included in the study, which also tested Hagen’s Cycle™, Aquarium Products’ Biozyme™, Aquatronics’ Bacter Plus™, Mardel’s A.C.T.™, Precision Aquarium Testing’s Sure Start™ and many others. Results showed that FritzZyme™ #9 Saltwater Nitrifying Bacteria was the only product to produce any testable decrease in either ammonia or nitrite in saltwater. By 14 days into the test, the FritzZyme™ #9 had reduced the ammonia level by over 70%. FritzZyme™ #7 Freshwater Nitrifying Bacteria had reduced the ammonia by over 60%. No comparable results were found with any other product tested. California State University performed further testing, researching why FritzZyme™ produced such superior results. Electron microscope pictures showed that FritzZyme™ was the only product to form large, uniformly developed bacterial mats on bio-media. Products showing slight ammonia reduction created small, broken bacterial mats. Those showing no ammonia reduction never produced colonized cultures on media. Clearly, the difference was in the bottle: FritzZyme™ contained large, concentrated true nitrifying cultures.

TurboStart™ is concentrated FritzZyme™. It gives nitrification an even larger boost by introducing over thirty million live nitrifying bacteria per ounce, rapidly accelerating the nitrification process. Ammonia and nitrite are quickly reduced to safe levels. Both ammonia and nitrite are reduced by over 90% in less than 5 days. Fish stress (induced by high levels of ammonia and nitrite) is also reduced and moralities normally associated with "New Tank Syndrome" are eliminated. Just follow the easy lab-verified starter plan!


Many products that don’t effect ammonia or nitrite claim to contain nitrifiers, causing confusion among hobbyists about nitrifying bacteria. The misinformation presented in ads and product labels hides the fact that most of these products actually contain species of heterotrophic Bacillus and Pseudomonas bacteria - NOT nitrifiers. This is why they don’t work. True nitrifying bacteria belong to the Nitrobacteraceae family. Nitrifiers are strictly aerobic autotrophs which utilize inorganic (without carbon) compounds as their primary energy source (specifically ammonia and nitrite). Five genera are accepted as ammonia-oxidizers and four as nitrite-oxidizers. Identified to grow naturally in both wild environments AND in the bio-filter in captive freshwater systems, Nitrosomonas (ammonia-oxidizers) and Nitrobacter (nitrite-oxidizers) are the most well known. Marine nitrifiers (Nitrosococcus and Nitrococcus) are different from the freshwater nitrifiers but are closely related. Though several products claim to contain these nitrifiers, very few actually do.

Many companies package spore-forming Bacillus bacteria and claim that the bottle contains nitrifiers. These products always have a long shelf-life (greater than 7 months). Since true nitrifiers are not spore-forming, products containing true nitrifiers always have a short shelf life. In this way, it is easy to determine when an "imposter bacteria" is masquerading as a nitrifier; it will either not have a posted shelf life, or the shelf life will be longer than 7 months. All dry product formulations claiming to contain nitrifiers use blatant false advertising. These products consist of sludge-eaters in their spore stage. Dry formulas can NOT contain nitrifiers; since true nitrifiers are not spore forming, they cannot be dried into powdered products. Any microbiologist will confirm this fact. Nitrifiers cannot survive the drying or freeze-drying process; they will not maintain any valuable culture or inoculate. Other products recommend the addition of gravel, bio-media or water from an established aquarium. This is usually the only source of nitrifiers with their method; the product itself usually contains trace elements and chemicals. An element of risk is involved when adding water or media from another system, as there is a large risk of introducing ich, velvet and other pathogens. When using competitive products containing heterotrophs (not nitrifiers), the nitrogen cycle basically follows the same course as when no bacteria are added at all and the system cycles naturally. The cycle with these products still normally lasts 30 days in freshwater, and up to 60 days in saltwater. Hobbyists often lose fish as they desperately wait for the cycle to finish. Hobbyists and experts who have used these deceitful products in the past are understandably skeptical about FritzZyme™ and TurboStart™. But laboratory testing has shown how FritzZyme™ and TurboStart™ are different. Results are incomparable.


Full Article:

[D24]

Nitrifying Bacteria - Author: Laura Muha (Tropical Fish Hobbyist Magazine)

One of my greatest fears—at least as far as this column is concerned—is that someday a deadline will be looming, my editor will be lobbing terse emails my way (“Are you planning to turn in your column any time this century, Laura? Please advise.”), and I’ll be panicking at my computer because I have run out of ideas.

Like most columnists, I do keep a list of potential topics, and I’m in no danger of scratching off the last item anytime soon. But that nagging fear persists, which was why I was so happy to get an email from Eric Linthicum, a cichlid keeper from Tucson, Arizona.

Linthicum asked whether I would consider doing a column on establishing and caring for the nitrifying bacteria that make up an aquarium’s biological filter. “I’ve noticed as I read magazines, books, and websites that the advice and rules given by experts and novices alike are inconsistent,” he wrote. “Some folks feel these bacteria are almost indestructible (rinsing in chlorinated water is okay, will live for several hours out of water), while others treat them as most delicate (never rinse in anything but old tank water, can only live for minutes outside of water). Also, how long they actually live and how quickly they migrate to new objects and colonize seems to be a matter of much speculation.”

Linthicum didn’t have to convince me the topic was worth exploring. How many times had I been told that I should only vacuum half the gravel in my tank gravel at a time to prevent sucking up too many nitrifying bacteria? And what about antibiotics? Could they wipe out a biofilter, or are they—as the package inserts that come with aquarium medications insist—harmless to nitrifying bacteria?

“Sometimes one article even contradicts the next in [the same] major periodical,” Linthicum pointed out. “And there is a reason for this, I think: most of the information is anecdotal. You just don’t see a lot of references to scientific, objective studies of the life cycle of these bacteria, at least as they pertain to pet fish…I’m sure you’re talking to some real scientists, so I’ll be interested in getting some concrete answers!”

He wasn’t the only one. Like Linthicum, I’ve long been fascinated by the microscopic organisms that make up an aquarium’s biofilter. They process organic debris that would otherwise build up in the water and sicken or kill the fish, so our success as aquarists depends on them. Yet we can’t see them, can’t count them (at least not without the high-powered microscopes few of us have access to), and even the people who study them for a living can’t agree on what they are.


Nitrifying Bacteria
For years, scientists assumed Nitrosomonas (sometimes referred to as “Nitrosomas”) were the bacteria responsible for breaking down ammonia in aquatic systems and Nitrobacter were responsible for oxidizing nitrite. That’s because when aquarium bacteria were cultured in the laboratory, those two species tended to predominate.

But the lab environment tends to select for particular bacteria, says Dr. Peter Strom, a professor of environmental sciences at Cook College in New Jersey. Strom has been studying nitrifying bacteria in wastewater treatment for more than 30 years. That’s because the lab environment selects for particular bacteria. So while Nitrosomonas and Nitrobacter grow quickly in the lab, that doesn’t mean they’re doing most of the nitrification in the natural environment, he said.

Indeed, in recent years studies published in academic journals have suggested that other bacteria, most notably a species known as Nitrospira, may actually be handling much of the nitrification in fish tanks. “Bottom line is this: there are a lot of species of bacteria that will feed on nitrogen compounds,” said Thom Demas, curator of fishes at the Tennessee Aquarium in Chattanooga, the world’s largest freshwater aquarium. “It’s most probable that there are many bacteria responsible for the nitrogen cycle in any given place at any given time.”

Regardless of which bacteria are involved, it’s important to realize that they, all living things, evolve and adapt to their environment. And because each tank represents a self-contained ecosystem, ever so slightly different than that of any other tank (and that includes the one sitting next to it), the microorganisms within it are likely to evolve with the slightest difference as well. “If you have a tank that has been established for a few months, some of us feel it will have evolved its own unique organisms that have become very well adapted to that environment,” Strom explained. “If any one of them has a slight advantage, it will outcompete the others. After one year are they different species? You could have arguments about that.”

Arguments aside, the two things every aquarist has to worry about when it comes to nitrifying bacteria are establishing them and maintaining them.

I discussed the former at length in earlier columns on cycling an aquarium (TFH, June and July 2005), so for the purposes of this article, suffice to say that nitrifying bacteria seem to be present in all aquatic environments, including new aquarium setups. But in such tanks, there won’t be enough of them to process the waste produced by a full load of fish; asking them to do so would be the fish-tank equivalent of asking a small-town wastewater treatment plant to suddenly take on all the sewage produced by New York City.


Cycling
In order to avoid major problems, the facility—in this case the bacterial colonies—must first be expanded, and you do that by providing them with their favorite energy source, ammonia. As they oxidize it, two things happen: they begin to multiply, and they also produce nitrites, which provide an energy source for the second key group of bacteria, the nitrite oxidizers, which also multiply. When both colonies are large enough to handle all the waste produced in the tank, it is considered “cycled,” meaning the biofilter has been established.

How long this takes to occur varies considerably, from as little as 21 days to as long as six weeks, but under any circumstances, nitrifiers are slow growers as compared to many other bacteria. For instance, E. coli bacteria double in number every 20 minutes, but the fastest growing nitrifiers take eight hours to do the same, said Strom.

In my earlier columns I explored the variables that impact this, among them water temperature, oxygen levels, the presence of stressors such as heavy metals or pollutants, and the amount of food available.

The reason those variables are worth bringing up again here is because they also affect the long-term well-being of the bacteria in the biofilter. In addition, nitrifying bacteria are sensitive to ammonia. So ironically, even though they require it to grow and multiply, too much will have the inverse effect, said Demas.


Die-offs
Each species also has a temperature range within which it grows best. If the temperature strays outside that range, bacterial growth slows down. Fish ponds are a case in point; in colder climates, most of the nitrifying bacteria die off over the winter, so the biofilter must be re-established each spring.

Likewise, a drop in oxygen—which can occur if the water becomes too warm or a power outage disrupts its circulation—can destroy some of the bacteria. And even a buildup of debris in the filter can cause problems, because it increases the tank’s bioload and also slows the turnover of water in the tank. “The reduced flow [means] less water through the bio-filter, which means less ammonia/food for the bacteria, resulting in a decrease in the bacterial count,” Demas explained.

Poor tank maintenance can affect bacteria in another way, as well, because the acids that are a byproduct of nitrification build up in the water. At first they’re neutralized by the buffering capacity of the water. But over time this is depleted, and if not replenished through a water change, the pH of the water begins to drop, which stresses not only the fish, but the bacteria. “A pH of 6 is really quite inhibitory to nitrifying bacteria, and 5.5 would be the absolute cutoff,” Strom said. “There wouldn’t be any of the traditional nitrification below that. Even 6.5 slows them down.”


Tank Maintenance
But what about the impact of tank maintenance itself on aquarium bacteria? Bacteria grow on surfaces such as aquarium glass and gravel, so what happens when we scour the sides of a tank with an algae magnet, or clean the bottom with a gravel vacuum? I’ve been told on a number of occasions that vacuuming more than half the tank bottom at a time could remove so many bacteria that the system could go into a secondary cycle.

Nonsense, says Strom. He explained that within hours of the time the bacteria begin growing, they lay down what’s known as a biofilm (“we used to call it a slime, but ‘biofilm’ sounds much more scientific!” Strom jokes) essentially gluing themselves to whatever surface they’re growing on. Over time, this biofilm can get quite thick, and in streams and other fast-moving bodies of water, its outer layers are sometimes peeled away by the force of water passing over them. But the tug of water through an aquarium siphon is too weak to have that effect, and even if it did, there would still be plenty of bacteria left behind to handle the tank waste. “Powerwashing wouldn’t get them all off!” Strom assured me.


Antibiotics?
One of the last subjects I wanted to tackle in relation to aquarium bacteria is antibiotics, but before I do, I want to stress that I’m not a proponent of their use—at least not without an extremely good reason and an extremely good diagnosis. As I explained in an earlier column (TFH, December 2004) adding any drug to a tank can set off a complex series of chain reactions that can have unintended consequences for fish, partly because of the fish’s unique physiology, and partly because of the way most of the drugs are delivered.

While most drugs for humans and animals are typically delivered orally, topically, or via an injection, nearly all over-the-counter fish drugs are added to the tank itself. That not only affects the osmoregulatory processes of the fish, but also the bacteria in the biofilter. “An antimicrobial by definition is a substance that is against microbial organisms—and what are the bacteria in your filtration system? Microbial organisms,” Dr. John Pitts, a veterinary consultant and former aquaculture veterinarian for Washington State, told me when I interviewed him for the earlier column. But, he added, “it does depend on the product…not every product does kill [nitrifying] microbes.”


A Newfound Respect
Before I started this column, I felt mystified and perhaps even a little intimidated by the invisible microorganisms on which my tanks depend. As I wrap it up, I realize I’ve gained a new respect for them. They don’t ask much from us fishkeepers—just a place to live, food to eat, and a stable environment. But think of what they give us in return: healthy tanks for our fish to live in and for us fishkeepers to enjoy.

"... E. coli bacteria double in number every 20 minutes..." Not sure about that. I saw a test from PSB that left a culture of "Test organism" of 110 000 (bacterial cells inoculated per test piece) that grew to 8 800 000 in just 30 mins in lab conditions.