Ammonia. The mention of that word strikes fear in the heart of most ponders. Chemical symbol NH4, ammonia is a colorless gas which is readily soluble in water.

The Killer Among Us
Without a doubt, ammonia is the #1 killer of koi. Ammonia causes a stress reaction in koi while simultaneously suppressing the immune system. Because ammonia has a high affinity for hemoglobin, fish subjected to ammonia may show symptoms similar to those encountered in a low-oxygen situation (gasping, lethargy, seeking cooler with high aeration). Once the fish becomes stressed and is unable to rapidly assimilate oxygen, the animal starts to crash. Ammonia tox'ed fish in the crashing stage will usually sit motionless on the bottom and excrete a heavy coating of slime. For fish showing these symptoms, the end is near.

Ammonia Management
Fortunately, Mother Nature has done most of the dirty work of eliminating ammonia for us. Bacteria (Nitrosomonas) utilize ammonia as a food source, converting it into less-toxic nitrite... and eventually converting nitrite into nitrate. In an established koi pond, these bacteria thrive in the biofilter and coat the liner, plants, and even the fish themselves. Because of this abundance of bacteria, in a balanced pond ammonia is consumed as quickly as it is produced.

How Much Ammonia Is Too Much?
Simple answer: Any detectable amount of ammonia is cause for concern.

Ammonia Sources
Ammonia is excreted by fish via the gills, kidney, and anus. Fecal matter also outgases ammonia, as does decaying organic matter (dead plants, leaves, mulm).

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Ammonia Test Errors: Dechlorinator Can Affect Readings!

The Effects Of Dechlorinator On Ammonia Readings
One little "gotcha" lurking in the wings which is frequently missed by new ponders is the effect of certain declorinators on ammonia readings. An ammonia test conducted when dechlor is present will show incorrect readings. Water with no ammonia whatever may test positive for ammonia. Conversely, water with high ammonia levels can read as ammonia-free. My advice is to use a dechlorinator which is compatible with your ammonia test. Which are compatible? The only two I've had any luck with are AmQuel (which, in my humble opinion is the only first-rate dechlorinator on the market) and a salicylate-type ammonia test kit (Tetra Pond). There will still be a bit of interference, but it’s negligible.

If you want to see if you have compatibility problems with your particular test kit, run a brief test, as follows:
• Step 1: Fill a five gallon bucket with tap water. Test this untreated water. Keep this test sample as your untreated reference. It should show no ammonia.
• Step 2: Add dechlor to the bucket at the recommended dose. Test this water and compare it to Step #1. If there isn't any difference in color or turbidity (i.e., no "haze" is present compared to the treated sample), continue below.
• Step 3: Add 10 drops of household ammonia to the bucket. Stir well and test. If this sample shows positive and doesn't have any unusual haze, you've got a winner.
If your ammonia test kit fails any of the above steps, don't expect even remotely accurate results. Find another test kit.

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Nitrite (NO2) is an intermediate compound produced by Nitrosomonas bacteria acting on ammonia. In the on-going bioconversion of ammonia process, this is the second step toward detoxification of ammonia wastes.

Natural Born Killer
Nitrite is a highly under-rated killer of koi and goldfish. Because many pond-keepers do not understand the nitrification cycle, nitrite is frequently overlooked when fish begin to die for no visible reason. Nitrite is toxic to koi and causes immune suppression as well as nitrite poisoning (aka "brown blood disease"). While not as immediately toxic as ammonia, any measurable amount of nitrite should be cause for concern. Depending on pH, condition of the fish, temperature and other factors, long-term exposure to nitrite levels as low as 0.5 ppm can kill or lead to susceptibility to opportunistic pathogens. Fish subjected to nitrite may show symptoms similar to those encountered in a low-oxygen situation (gasping, lethargy, seeking cooler with high aeration). Nitrite-toxed fish will refuse food, clamp their fins, and exhibit fearlessness.

How Much Nitrite Is Too Much?
Simple answer: Any detectable amount of nitrite is cause for concern. While a transient level which exists for only a day or two is unlikely to cause any real harm, the cause needs to be tracked-down and fixed. Nitrite spikes are commonplace in low-pH / low-KH water where temperatures are cool (under 70F) and feeding is heavy.

Nitrite Sources
With the exception of certain plant food tablets, the only significant source of nitrite come from the Nitrosomonas bacteria species residing in the biofilter.

Nitrite Management
Again, Mother Nature has done most of the dirty work of eliminating nitrite for us. Bacteria (Nitrobacter) utilize nitrite as a food source, converting it into less-toxic nitrate. In an established koi pond, these bacteria thrive in the biofilter and coat the liner, plants, and even the fish themselves. Because of this abundance, in a balanced pond nitrite is consumed as quickly as it is produced.

Chemical Management
In some cases, we can't rely on Mom Nature to keep the nitrite level down or we may have thrown our biological filter bacteria for a loop thereby causing a nitrite problem. In these cases the addition of salt has the effect of temporarily masking the uptake of nitrite by the fish. Generally speaking, a pond salted to 0.3% (about three lbs of salt per 100 US gallons) will allow the survival of otherwise healthy fish in water containing 3-4 ppm of nitrite. Note that salt is not a cure-all. It is a band-aid. Salt gives you a couple of weeks to correct your nitrite problem properly... nothing more.

Copyright © 1998 by Roark. All Rights Reserved.
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One of the easiest measurements to make is water temperature. Sadly, it is also one of the hardest measurements to change. Fortunately, unlike fussy tropical fish, koi have a very wide temperature range and the absolute numbers are not all that important. Consistency of those numbers plays a more important role.

Acceptable Limits
Healthy koi can survive from 33F to 105F. Notice I said survive. At the extreme ends of the scale, koi tend to suffer. At the low end, they essentially shut-down to the bare minimum functions needed to support life. They sit on the bottom, cussing the weather quietly, and wait for better weather. In this mode, the koi is miserable. It is not hibernating. If disturbed, it will wake and sluggishly deal with whatever woke it. It has no immune system to speak of and is kept alive by the fact that few bacteria or parasites are capable of functioning below 45F.

At the high end of the temperature scale, koi will seek cooler water away from direct sunlight. Favorite hiding places are under the leaves of floating plants where they hover near the surface. Their metabolism remains very high, but because the dissolved oxygen level is nearing the critical level, the fish enters a state of elective rest to conserve what little oxygen is available.

Optimum Temperature For Growth & Health
For koi to thrive and grow, temperatures between 60F and 80F should be maintained. Depending on the fish, 74F to 76F is generally quoted as being textbook-optimal. Some breeders like to increase this a bit for maximum growth while others prefer cooler water. Like many things in ponding, there is no universally-accepted "perfect" temperature. If temperature fluctuations are not extreme and water quality is good, a range of 60F to 80F will yield healthy fish.

Purchasing A Thermometer
Depending on your budget, you can either purchase a cheap pool thermometer or get a nice digital one from Radio Shack. Personally, I like the Radio Shack variety which logs minimum and maximum temperatures for both the air temperature and the pond. Besides being very accurate, these things are pretty cheap. I think I paid $16 bucks for my indoor/outdoor logging unit a year ago. To be fair, while digital is nice, there is nothing inherently wrong with analog units constructed along the lines of a traditional glass bulb with expanding liquid. Floating pool-type thermometers are very cheap and can be calibrated to a good degree of accuracy. Unlike the floating aquarium-type units, pool thermometers are large enough that even the biggest koi cannot swallow them. There are reports of koi being killed when they ingested (and subsequently broke) glass aquarium thermometers. Remember that koi "mouth" everything in their environment so stay away from anything capable of being swallowed.

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Carbon Dioxide (CO2):

Of all the basic water quality parameters discussed by even advanced koi keepers, this is undoubtedly the most misunderstood and least-frequently tested water quality parameters out there. When folks with otherwise textbook-perfect water report sleepy or lethargic fish, or fish which don't seem to get excited by the thought of food, its time to get "up" on CO2. After verifying the "Fab Four" (pH, ammonia, nitrite and dissolved oxygen), you'd be shocked at how often this sneaky parameter upsets the applecart.

What is it?
Call it CO2, carbon dioxide, carbonic acid... whatever. Carbon dioxide is a heavy, colorless, odorless, acidic gas which is very soluble in water. At the molecular level, CO2 is composed of one carbon atom tightly bound to two oxygen atoms. When dissolved in water, it is properly called carbonic acid. In its "dry" state, it is simply called CO2.

CO2 Toxicity
To us humans, consuming water with a very high concentration of CO2 isn't a big deal. In fact, each time you pop the top on a can of your favorite soda, you are drinking water saturated with CO2. Because we humans obtain our oxygen from the air, orally consuming substantial amounts of CO2 produces few side effects beyond a mild headache. Fish on the other hand face a much different world. Instead of luxuriating in an atmosphere composed of 20 parts of oxygen for every hundred parts of total gas weight, they must survive in water which averages only about 8 parts oxygen per million. CO2 accounts for less than 1% of our atmosphere, yet in a pond the amount of CO2 can very easily exceed the O2 concentration. I have personally seen ponds with a measured concentration of 40 ppm CO2!

When you put all this into perspective, two things become clear:
• Koi and fish generally are some amazingly well adapted creatures. They have evolved superior means to extract oxygen at concentrations which are, from the human viewpoint, undetectable.
• If you plan on keeping koi with good success, you need to get a handle on the CO2 level.
Controlling The CO2 Level
I once had quite a lengthy discussion with a pond "expert" who was absolutely convinced that simply aerating a pond would drop the CO2 level to undetectable levels. On the surface, this makes sense: As you add oxygen to the water, the CO2 comes out, right? Not exactly. Take a peek at a graph I shamelessly stole from the fine folks at Aquatic EcoSystems.
Commercial plug: If you haven't been to their website at then you really should. Great company. Neat products. Lots of information free for the taking.)

What I've just told you is one of the best kept secrets in ponding: Don't try to strive for some low pH number. If you've got water that comes out of the tap in the 8.0 region, leave it alone. If the water is carbonate-poor, all you need to do is add some carbonate to it. With 80-120 ppm of KH in the water, you'll have a rock-steady pH and the CO2 level will be very low. You can grow some very serious fish in this water. Plants on the other hand are another matter.

As I've said before in these pages, in a perfect world, there would be koi ponds and plant ponds, and these two would remain separate entities. The CO2 number is one of those water parameters which places fish and plants squarely at odds with each other. Fish do well in water which has very little CO2. Any water supply which has less than 5 ppm of CO2 is acceptable, with ideal levels being between 0 and 2.5 ppm. Plants on the other hand can use dissolved CO2 as food and will actually do better with a CO2 level of 5 to 20 ppm.

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Carbon Dioxide Concentration -vs- pH / KH

Koi appreciate water with a CO2 level less than 5 ppm. As the amount of CO2 increases, the fish’s ability to respire CO2 in exchange for oxygen becomes impaired. Even in ponds where the measured O2 level is high, it is still possible to have oxygen stress occur. The table below shows the approximate CO2 level as a function of pH and KH (alkalinity).

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Dissolved Oxygen:
The atmosphere we breathe contains between 19% and 21% oxygen. Fish, like people, need oxygen to survive. The fact that oxygen is slightly soluble in water is what keeps our fish alive and well. By encouraging a high oxygen level, we help assure strong and healthy fish.

For oxygen to efficiently dissolve into water, several things need to happen:
• The water needs to be put into motion. By splashing, spraying, pumping or somehow agitating the water, we expose a larger percentage of the fluid to air. As the water near the air/fluid interface gains oxygen, it needs to be moved out the way so more water can be exposed. Think of adding a drop of food coloring to cookie dough. You must knead and turn the dough over again and again to get uniform dispersion of the coloring. This essentially is what moving water gives us.
• There needs to be a higher oxygen pressure on the atmospheric side of the air/fluid interface than there is within the fluid itself. This concept gets a bit technical but the basic idea here is this: For water to receive any additional oxygen, it needs to be oxygen deficient to start with. Once water reaches its saturation point, you'll find it nearly impossible to add additional oxygen (without resorting to chemicals or "sledgehammer" mechanical effects). The more depleted the oxygen supply, the more aggressively the water will attempt to absorb oxygen. This is why even gentle water motion during a power failure will often keep your koi alive and well for many hours.
Desirable O2 Levels
Koi are happiest in water with a dissolved oxygen level above 6 ppm. Anything above this number is glorious and will encourage rapid growth, ravenous appetite, and robust koi. Between 4 and 6 ppm, koi begin to exhibit signs of oxygen stress. Depending on the individual fish, some koi will start "hitting" the surface occasionally as the D.O falls below 5 ppm. By 3 ppm, nearly everyone will be standing on their tails with their noses in the air or congregating near areas of higher oxygen transfer (waterfalls, spitters, etc). If low oxygen levels persist, smaller koi will begin to die followed shortly thereafter by the larger fish. By 2 ppm, the quick death of everything in the pond is quite certain. Healthy koi can tolerate brief periods of 3 ppm living, but this is to be avoided at all costs.

Temperature Effects
The ability of water to carry oxygen is highly dependent on water temperature. As the temperature drops, more oxygen can be held until a point just short of freezing is encountered. At 37 degrees F, nearly 14 ppm of dissolved oxygen can be accommodated. Conversely, as temperature rises, water begins to lose its oxygen-carrying ability. At 85 degrees, O2 saturation is only about 7 ppm.

How To Kill Your Fish
All of the things below chip away at your oxygen budget. Some are obvious while some are subtle. All kill by the same basic mechanisms: Reduction of available oxygen at the gill/water interface or by inhibiting the uptake of otherwise available oxygen.
• Don't insure adequate circulation across the pond.
• Add oxygen-grabbing medications like formalin, potassium permanganate, or 0.6% salt during hot weather. (A 0.3% salt solution is generally not stressful).
• Add an overload of plants. Plants *consume* oxygen at night and cover the surface of the water, thereby reducing the surface area available for oxygen exchange... a fact the Green Police fail to tell their acolytes./li>
• Undersize your biofilter, restrict the flow to it, or use medications which kill the nitrifying bacterial within. As ammonia an nitrite levels rise, the fish’s oxygen uptake mechanism becomes impaired.
• Allow *any* level of ammonia to remain present in a cycled pond.

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Page rev 1.1 of 06SEP2000