Koi Pond with Zaap Pure UV bulb, Dainichi food, Kohaku, Motsuba, Tancho

Ammonia in your pond!?

Ammonia is a misunderstood and frightening aspect of managing pond water quality.

The primary source of ammonia is fish waste. The rate at which fish excrete ammonia is related to the feeding rate and protein level in the food. High protein and large amounts of food result in more ammonia. Protein is used by fish to produce muscle and energy while waste ammoni a is excreted through the gills.


Another main source of ammonia is the decomposition of organic matter at the bottom of the pond. Fecal solids excreted by fish, urine, dead plant material and uneaten food settle to the bottom of the pond where they decompose. this decomposition process produces ammonia which diffuses from the sediment into the water.


Ammonia is toxic to fish at high as well as low levels. At high levels of ammonia, fish will become lethargic and eventually die. At low levels they experience sub-lethal effects such as poor growth, poor feed conversion and reduced disease resistance at concentrations below the lethal level.


Ammonia exists in equilibrium in two forms; ammonium ion NH4+ and free ammonia NH3. Ammonia in water is either un-ionized, toxic, free gas (NH3) or the non-toxic ammonium ion (NH 4+). Most test kits measure total ammonia which is the sum of both forms. Un-ionized ammonia is most toxic above pH 8.5 and at temperatures above 86°F. As the pH increases, the ionized NH4+ is liberated into gaseous NH3.See the Fig. below that illustrates the relationship between temperature pH and % of un-ionized toxic ammonia.


Unlike humans, which excrete reduced nitrogen within their urine waste stream, fish release reduced ammonia-nitrogen through the gill structures. As with the transfer of oxygen into, and carbon dioxide out of, our lungs, this transfer of ammonia across the surfaces of fish gills is driven by a concentration gradient (i.e., moving progressively from a high concentration on one side of the gill [inside] to a low concentration on the outside surface). However, this transfer inevitably slows down as the magnitude of this gradient decreases. Indeed, as the external concentration of free ammonia rises, a fish will accordingly have a harder time releasing ammonia...at which point its internal blood level of free ammonia will then rise.

In ponds, pH fluctuates with photosynthesis which increases pH and respiration which reduces pH. Therefore, toxic ammonia predominates during the late afternoon and early evening. The equilibrium between un-ionized toxic ammonia (NH3) and the non-toxic ammonium ion (NH4+) is also affected by temperature and salinity. At any given pH, more toxic ammonia is present in warmer water.


Under normal conditions NH3 (ammonia) and NH4+ (ammonium) will both be present in pond water. The two exist at an equilibrium point that is governed largely by pH and temperature. As the pH increases the ionized ammonia (NH4+) is liberated into the toxic gas (NH3). This relationship requires careful consideration of ammonia levels when adding baking soda to raise alkalinity. If you have high levels of ammonia, something is wrong and you must correct the deficiency.


The root cause of high toxic ammonia (NH3) can be any one of the following:

  1. Over stocking or stocking too quickly.

  2. Overfeeding

  3. Dead fish, plant material or food in the pond

  4. Filtration is not working correctly or is not properly sized

  5. Over cleaning filters might have killed or removed the beneficial bacteria colonies

  6. Water used for changes must have a similar or lower pH than the pond or NH4 may be converted to toxic NH3 from a pH increase. The addition of Amquel +may be required.

Common ways to remove or control ammonia:

Short term (instantly remove ammonia)

Water changes - this is by far the fastest and most reliable method but care should be taken not to stress the fish or add unsafe water

Ammonia-removing chemicals - there are many ammonia-removers on the market such as Amquel + concentrate or Zeolite, know what you are using and follow the reccomended dosages.

Long term

  • Increase biological filtration

  • Decrease feeding

  • Remove debris

  • Reduce fish load

  • Add beneficial bacteria such as Microbe-lift PL

Ammonia testing

There are a number of ways to test for NH3 and NH4 in the aquarium, probes and dip strips are still uncommon and most people use liquid test kits. These occur in two main types liquid ammonia test kits:


Nessler kits have one reagent, that is, a single bottle of liquid or one tablet to dissolve in your water sample. If your ammonia test kit registers in shades of amber, it's Nessler. They generally are quicker to use, but ammonia-locking products (e.g., AmQuel) will cause Nessler kits to give false positive readings. Nessler test kits measure ammonia NH3 and ammonium NH4. This is important to note and often missed as you will need to use a look up chart so see NH3 levels.


New Salicylate based tests, with two sets of reagents measure total ammonia (NH3+NH4). If your ammonia test kit registers in shades of yellow to green to blue, its salicylate. Salicylate test kits are unaffected by AmQuel and similar products.

Seachem Ammonia Test kit


This kit measures total (NH3 and NH4+) and free ammonia (NH3 only) down to less than 0.05 mg/L and is virtually interference free in marine and fresh water. This kit may be used with freshwater or marine water. Unlike other kits on the market, the chemical basis for this test assures that interference from other substances is highly unlikely


Using Seachem Prime?

Seachem logo, black and white shield logo

Testing for ammonia with the test kits above might produce false readings after a water change if you add to much de chlorinator. Seachem's Prime conditioner will give false readings for ammonia, on both Nessler's Reagent and salicylate tests. Sodium thiosulfate, Na2S2O3, in Prime reacts with the chloride ion that is part in the test reagents. According to Seachem after 24 hours you will then be able to test again and get accurate readings.

An alternative is to use a Seneye device which will constantly measure the toxic ammonia in your aquarium or pond.


Questions email: john@blueribbonkoi.com 

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