Essential Information about water quality and filtration for a healthy aquarium.

Below is a compilation of information from Dr. Timothy A. Hovanec's library articles on water quality and filtration. Dr. Hovanec is formerly the Chief Science Officer of the Aquaria Group of Marineland. He now has his own company Dr Tim's Aquatics. Dr Hovanec, in his dissertation, identified the bacteria responsible for converting ammonia to nitrite and then to nitrate. Numbers in parentheses indicate which article the information was pulled from. Links to articles cited are at the bottom of this page.

Topic Index:

• Nitrifying Bacteria
• Heterotrophic Bacteria
• Water Quality
  • Ammonia
  • Nitrite
  • Nitrate
  • pH
  • Alkalinity (KH)
  • Total Hardness
  • Phosphorus
  • Dissolved Oxygen
  • Dissolved Solids
  • Temperature
  • Turbidity
  • Chlorine
• Filtration
  • Mechanical
  • Biological
  • Chemical
• Citations

Nitrifying bacteria (Nitrospira)

• Newly discovered species of Nitrosomonas (not Nitrosomonas europaea) convert ammonia to nitrite in aquaria (10).
• Nitrospira converts nitrite to nitrate. It slower-growing than Nitrosomonas and growth is further retarded by initial high levels of ammonia. May take up to 3 weeks for Nitrospira to become established in a new tank. (6) Nitrobacter, which was thought to be the genus of nitrite-oxidizing bacteria in aquaria, are not found in aquaria. Instead, Nitrospira, which is a new phylum of bacteria, have been shown to the nitrite-oxidizing bacteria (10, Dr. Tim Hovanec, electronic mail, 12/29/03)
• are Autotrophs (get the carbon they need from carbon dioxide) (1)
• do not work as efficiently below pH 6.0; prefer a pH of about 7.8. (6)
• grow in colonies, preferably on (highly oxygenated (1, 6)) surfaces (4)
• the media on which they grow must be clean of organic debris, and the levels of DOC (dissolved organic compounds) must be low (4) In mechanical filters there may be cycling of nitrifying populations as they increase when the area is clean and decrease as the area clogs. (7)
• the oxidation and reproduction rate of the bacteria is directly tied to the water temperature. The colder the water, the slower the bacteria work (7)
• can double population every 27 to 33 hours in good conditions (1) the nitrifying bacteria are slow growing so it takes them several days to start converting appreciable amounts of ammonia to nitrite. bacteria which convert nitrite to nitrate (the nitrite-oxidizers) are even slower growing than the ammonia-oxidizers. (3)
• In a 24 hour period, a single nitrifying bacterium will double forming two bacteria. In that same time period, a single heterotrophic bacterium can reproduce to a population of 2,361,183,241,434,820,000,000 bacteria (7)
• are aerobic and need plenty of oxygen to grow. To a degree the more oxygen available to the bacteria the faster they can convert the ammonia or nitrite. The biological filter should be in an area where the water has plenty of oxygen or suspended in the air where the water can trickle over the media and mix with oxygen from the air. (1) Oxygen is of prime importance. The rate at which an individual or colony of nitrifying bacteria can oxidize ammonia is determined by the amount of oxygen which is available. (6)
• Using ammonia binder/removers: the detoxified ammonia is still available to the ammonia-oxidizing bacteria which convert it to nitrite. requires use of a salicylate-based ammonia test kit (6) Most people assume that the number of nitrifying bacteria increases in direct proportion to the amount of ammonia produced in the aquarium. Actually, in a scientific sense, this might not be the case. It is not known for certain whether continuing to add ammonia means that the population of nitrifying bacteria continually increases, or if the numbers level-off and those bacteria work more efficiently. More efficient is defined as the same number of bacteria oxidizing more ammonia in the same amount of time. (7)
• Bio Spira from Marine Labs contains Nitrosomonas, Nitrosospira and Nitrospira. While it is best if refrigerated until used, recent research has shown that it has a 6 month shelf life at room temperature (Dr. Tim Hovanec, electronic mail, 12/29/03). It can not be overdosed. Repeated dosing of your aquarium with ammonia removing liquids (such as BIO-Safe, Amquel, Ammo-lock and Aqua-Safe) can inhibit the beneficial action of BIO-Spira. Ammonia removing liquids should only be used to initially treat tap water. It is normal to have a small (<2 ppm) amount of ammonia or nitrate during the first few days after set-up. These concentrations are not harmful and will quickly drop to zero with proper use of BIO-Spira. (8) Optimal conditions for Bio Spira: Water Temperature: : 60°F-87°F (15°C-31°C) pH: range between 7.0-8.5 Within 24-48 hours, the bacteria will attach to the BIO-Wheel®, gravel, or other surface in the tank and your water should be clear. Don't use antibiotics. No UV light filters or proteain skimmers for 48 hours. (9, Dr. Tim Hovanec, electronic mail, 12/29/03)

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Heterotrophic bacteria

• are responsible for the break down of organic materials, e.g. leaves, fish feces (1)
• are one of the chief producers of ammonia in an aquarium (1)
• are responsible for bacteria bloom which turns the water milky white (1)
• can double their population every 20 minutes and can grow over and smother nitrifying bacteria (1, 7)
• Nitrification produces hydrogen ions which are neutralized by the compounds which make-up alkalinity (chiefly bicarbonate). But once the alkalinity has been consumed, the hydrogen ions accumulate and the pH drops. (1)
• consume oxygen which may inhibit growth of the nitrifying bacteria (1) especially if there are large increases in organic matter in the tank (6)

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Water quality:

• Should be tested regularly and logged. (2)
• The goal should be stability as fish do not tolerate sudden changes well (2)
• Don't overcrowd tank with fish (4)
• Don't overfeed (4)
• Rinse filter weekly in dechlorinated water(4)
• Regular partial water changes (4)

According to Dr. Tim (electronic mail, 12/29/03), Freshwater indicators, with some exceptions depending on fish species, should be:
Ammonia: <0.1 ppm
Nitrite: <0.1 ppm
Nitrate: <50.0 ppm
pH: 6.0 - 9.0
Alkalinity: 0 - 3 mEq
Total Hardness: 0 - 200 ppm CaCO3
Dissolved Oxygen: >7.0 ppm
Total Dissolved Solids: 50 - 2,000 µS/cm
Chlorine: <0.01 ppm
Temperature: 72 - 86 deg F

red=Critical Water Quality Factor

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• Ammonia
  • Critical factor for fish health (2)
  • exists in water in two forms: the ionized (NH₄⁺) called "ammonium", and un-ionized (NH₃) called "ammonia". The overall ammonia level in the water is the sum of these two forms. Research has shown that it is the un-ionized form that is toxic. (6)
  • As pH increases, a greater percentage of the total ammonia becomes the toxic un-ionized form. (6)
  • is the principal excretory product of most aquarium organisms. (2)
  • is also formed by heterotrophic bacteria digesting organic matter (2)
  • Ammonia toxicity damages the nervous system of fish. Symptoms include: darting back and forth in the tank in uncontrollable spasms, spinning in small circles, and finally laying on the bottom before dying. (6)
  • should be maintained below 0.1 mg/L (< 0.1 ppm) (total ammonia) in the aquarium. (2)
  • In a new tank, ammonia increases rapidly over the first 3 to 5 days, then starts to decrease and is usually zero by day 10. (6)
• to reduce ammonia
  • rinse the mechanical filter media often (2)
  • minimize organic matter (from fish poop and excess feeding) (2)
  • partial water changes (2)

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• Nitrite
  • Critical factor for fish health (2)
  • exists in two forms, nitrite and nitrous acid. At lower pH values (below 8), a greater percentage of the total nitrite exists as nitrous acid (which is the toxic fraction). at the pH values commonly found in tropical fish aquaria (6.5 to 8.0), the majority of the nitrite is in the toxic fraction. (6)
  • Can be more toxic than ammonia. 3 to 5 mg/l (3-5 ppm) can kill fish in freshwater (6)
  • is formed either by the oxidation of ammonia (nitrification) or the reduction of nitrate (assimilatory nitrate reduction).(2)
  • should be maintained below 0.1 mg/L (< 0.1 ppm). (2)
  • kills fish by impeding the circulation of oxygen from the gills to the rest of the fish (3)
  • Any sudden increase in the nitrite concentration of an established aquarium is cause for immediate concern. The filter should be checked and serviced when high nitrite is detected. partial water change reduces nitrite levels. (2) In a new tank, 25% water changes every 2 or 3 days for the first three weeks (3)
  • In a new tank, nitrite levels remain in the toxic range and may stay high for 3 weeks or longer. (4)
  • When the nitrite level drops, the biological filter is "established." (4)

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• Nitrate
  • end product of nitrification. (2)
  • should be maintained below 50 mg/L (measured as NO3--N) (2)
  • reduce by partial water changes and growing live plants in the aquarium. (2)
  
   
• pH
  • is the measure of the hydrogen ion concentration in water (2)
  • the continued addition of acid (via nitrification) causes the pH to always tend to drop. (2)
  • most freshwater fish can tolerate a change of up to 3 or 4 full pH units (between pH of 5 and 9) (depending upon the time interval and the particular fish) but best not to go below 6 or above 8.4 for most freshwater fish (2, Dr. Tim Hovanec, electronic mail, 12/29/03)

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• Alkalinity (KH)
  • is the buffering (acid-neutralizing) capacity of water. Buffering is the capacity of the water to accept acids without a drop in pH. (2)
  • Eventually alkalinity will be depleted and the pH will drop quickly. Alkalinity must be periodically replenished with regular partial water changes (assuming the make up water has alkalinity) Common baking soda - sodium bicarbonate - will increase alkalinity. (6)

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• Total Hardness (GH)
  • is the sum of the calcium and magnesium in the water. (2)
  • For freshwater aquaria, total hardness is not generally a concern unless your water is at one extreme and the fish you wish prefer water at the other extreme (2) or you are medicating. Soft water (less than 50 mg/L CaCO3 will increase the toxicity of some medications so you need to use less. Read the label and follow the manufacturer's directions. (Dr. Tim Hovanec, electronic mail, 12/29/03)
  • Most fish can tolerate a wide range of hardness values (2)
  • to lower use ion exchange resins. (2)
  • to increase add calcium and magnesium. (2)

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• Phosphorus
  • is a nutrient for algae and plants. A large amount of pHosphorus in an aquarium can lead to algae blooms. (2)
  • is not toxic. (2)
  • partial water change, reduces phosphate, if make-up water is phosphorus-free (2)
  • test kits only measure soluble reactive Phosphate (also called orthophosphate) but much phosphate is bound to organic matter and not measured by these test kits. (2)

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• Dissolved Oxygen
  • is the most critical water quality characteristic (2)
  • Chronic low levels of oxygen lead to stress and secondary bacterial infections. (2)
  • The amount of oxygen water can hold depends mostly upon the water temperature and salinity. Higher temperature and higher salinity--less dissolved oxygen (2)
  • most effective way to increase the oxygen concentration in water is to agitate the water surface. While bubbling air in the water does work, it is not as efficient as vigorous surface movement. (2)
  • A fish that is suffering from lack of oxygen will usually first be at the water surface gulping for oxygen. (6)

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• Total Dissolved Solids (TDS) and Dissolved Organic Carbon (DOC)
  • is a measure of the amount of ions dissolved in the water. (2)
  • DOC is a measure of the dissolved organic carbon in the water (Dr. Tim Hovanec, electronic mail, 12/29/03)
  • Over time, the TDS will increase due to increased dissolved substances from feeding, water evaporation and other processes.
  • Regular partial water changes reduce TDS (2)
  • High levels of DOC can inhibit nitrification and can increase the biochemical oxygen demand (BOD) which in turn reduces the amount of oxygen in the water that is available to the fish and invertebrates). (2)
  • Need well-equipped water quality testing laboratory to measure DOC. (2)

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• Temperature
  • is a critical factor (2)
  • tropical fish 72-86 (Dr. Tim Hovanec, electronic mail, 12/29/03)
  • Tropical fish do not tolerate quick temperature changes (2)

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• Turbidity
  • not a critical factor (2)
  • too much turbidity can coat the gills of the fish and they could suffocate. (2)
  • reduce with mechanical filtration and water changes. (2)

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• Chlorine
  • is a critical factor (2)
  • can quickly kill fish even at very low levels. (2)
  • remove prior to addition to aquarium with commercial products. (2)

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Filtration

• Mechanical
  • traps particulate material (e.g. uneaten food, feces, plant material, etc) that contribute to water cloudiness (turbidity) (4)
  • rinse weekly as the organic matter provides a home for heterotropic bacteria that consume oxygen and produce ammonia. (4)
  • a smell like rotten eggs is an indication that the filter has been too long between cleanings and the filter has become anaerobic--hydrogen sulfide can kill fish. The entire filter must be cleaned immediately and the media changed. (6)

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• Biological
  • nitrification--conversion of ammonia to nitrite, then nitrite to nitrate, by bacteria. (6)
  • the most efficient types of biological filters, called wet/dry filters, take advantage of the fact that the bacteria need only intermittent contact with the ammonia-laden water. (4)
  • If the biological filter becomes clogged, the nitrifying bacteria cannot get the oxygen they need and are crowded out by other types of bacteria

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• Chemical
  • activated carbon (4)
  • removal of dissolved substances (dissolved organic compounds DOC (5) by chemically or pHysically binding them to the filter media.
  • mechanical filter on intake side of chemical filter. (4)
  • need good surface area between water and chemical filter (4)
  • replace when used up (water yellowish-brown or water is fishy-smelling-phenol (6)). carbon lasts about a month (4) depending on load on the tank (5)
  • the best carbon is bituminous coal based carbon because it has the right mix of pore size and internal surface area such that they remove more pollutants per gram of carbon than any of the other types. (5)
  • does not remove ammonia, nitrite or nitrate (5)

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Citations:

Note: These articles were formerly hosted on the Marineland website. Dr Tim's articles are now located on his website.

1. What Is: Denitrification?
2. Water Quality: A Holistic Approach
3. Technically Speaking: The First 30 Days
4. A Primer for the Beginner Setting Up a Fishtank
5. Activated Carbon
6. Basic Filtration for the Home Aquarium
7. Biofilter Surface Area: It Must Be Effective
8. The Bio Spira product
9. Marineland Frequently Asked Questions (FAQs)
10. What Is: Basic Aquarium Microbiology?