Basic Water Quality Limits
Water Quality: What is it?
It’s a funny thing. When dealing with sick fish you'll often hear someone say "maintain excellent water quality" as part of the treatment. Likewise, you'll hear "my water quality is perfect". But what exactly are the acceptable limits of each water quality parameter?
pH:
Generally speaking, koi will thrive in water which is maintained at a pH between 6.8 and 8.6. If you are accustomed to maintaining fussy tropicals, this huge of a pH range may seem counter-intuitive... but its real. Koi will quickly adapt to whatever reasonable pH you throw at them. More important than the actual pH value is the stability of the pH. A day-to-night and day-to-day variation of 0.3 pH points should be considered the maximum allowable. Common wisdom has it that a significant pH fluctuation from morning to evening is "normal" and "healthy". This is not true. A significant fluctuation is generally indicative of sagging carbonate levels, insufficient aeration, or an unhealthy fish load.
For an in-depth discussion of pH see pH.
Carbonate Hardness or Total Alkalinity (KH)
Also called "buffering capacity", this water parameter is overlooked by better than 90% of koi hobbyists. The measurement of the carbonate levels provides a direct indication as to the buffering characteristics of your pond water. Generally speaking and within reason, more KH is better. Koi will tolerate a very wide range of KH, but they tend to suffer from pH-induced stresses as the KH drops below 40 ppm. KH is optimally kept between 80 to 120 ppm, but again, koi are hearty animals and will tolerate very high KH's (up to 300 ppm) with no ill effects. Any KH measured below 40 ppm demands attention, for a pH crash is lurking in your immediate future.
For an in-depth discussion of KH see Carbonate Hardness.
General Hardness (GH)
General Hardness is a measurement of dissolved minerals, principally calcium and manganese. Unlike KH, GH has no significant buffering effect. Koi appreciate a GH-rich water from which they are able to assimilate calcium for strong bones. Especially in the case of fast-growing fry, ample calcium should be provided. Generally speaking, koi will suffer if the GH is less than 80 ppm.
For an in-depth discussion of GH see General Hardness (GH)
Ammonia
Ammonia is a highly toxic compound produced by fish as a result of their digestion of protein. Any detectable ammonia in an established pond is cause for immediate concern. To be sure, more fish are killed by ammonia than from all other factors combined. The maximum allowable ammonia reading is zero.
In a new or uncycled pond, ammonia will be present in significant quantity until the biofilter populates with sufficient quantities of nitrifying bacteria. The amount of ammonia which can be tolerated is dependent on several factors:
1. The pH: Higher pH's cause a greater percentage of ammonia to exist in the toxic, un-ionized form. This is not to suggest that dropping a ponds pH in response to an elevated ammonia level should be tried. Indeed, fish which are already ammonia-stressed will not generally tolerate a significant pH change.
2. Temperature: Higher temperatures increase the effects of ammonia toxicity. Elevated temps also reduce the oxygen level while simultaneously increasing the output of the fish’s metabolic wastes.
3. Oxygen Level: Maintaining oxygen levels at the saturation point tends to somewhat offset the effects of ammonia. Low oxygen levels combined with ammonia at any level will kill fish in droves.
4. General Health Of The Fish: Strong, healthy fish can tolerate a significantly elevated ammonia level for a short time. Fish which are weak, stressed, or carry a considerable burden of pathogens (flukes, etc) will tolerate ammonia poorly if at all.
For an in-depth discussion of ammonia see Ammonia (NH4).
Nitrite
Nitrite is the intermediate step in the bioconversion process. Ammonia is converted into nitrite before being again converted into nitrate. Nitrite, like ammonia, is highly toxic to fish. Like ammonia, the only acceptable number is zero.
For an in-depth discussion of nitrite see Nitrite (NO2).
Nitrate
Nitrate is the final product of the bioconversion process. Once thought to be harmless to fish, new studies are showing that nitrate may be considerably more toxic than originally thought. The maximum recommended nitrate level is 40 ppm where adult fish are kept and 10 ppm where fingerlings are present. There is no minimum level although zero would be desirable in the absence of plants.
For an in-depth discussion of nitrate see Nitrate (NO3).
Temperature:
Tough little campers they are, koi will tolerate temperatures from 33F to over 90F if the change occurs slowly and sufficient oxygen is provided. For best growth, water temperatures should be maintained between 68F and 78F. At these temperatures, koi will display excellent appetite and immune function. A steady temperature is more important than any absolute temperature. Koi routinely exposed to temperature fluxuations of more than 7F per day may become prone to various ills and show signs of stress. There is considerable evidence which suggests even a 3F change per day can interfere with best growth and color.
For an in-depth discussion of temperature see Temperature.
Oxygen
Dissolved oxygen levels in excess of 6 ppm are needed to successfully keep koi. Below 6 ppm, there is little room for error and any stress or disease may result in mortality. Having said this however, it is interesting to note that healthy koi can tolerate 3ppm O2 for short periods. Because it is very difficult to over-oxygenate a pond, most ponders attempt to keep the oxygen level at the saturation point. Generally speaking, it’s very difficult to over-saturate a pond.
Carbon Dioxide
Carbon dioxide (CO2) is a byproduct of normal fish respiration and is also produced by plants at night when photosynthesis has stopped. Koi need water relatively free from CO2 for best growth, health and color. In a perfect world, CO2 levels would essentially be zero but the effects of plants, carbonates, pH and aeration factors all contribute to a measurable CO2 level. For koi, CO2 levels must be maintained less than 5 ppm with values less than 2 ppm being ideal. Above 10 ppm, lethargy and loss of appetite will occur. By 50 ppm, the fish enters a stuporous state and cannot respond to most external stimuli. Most ponds (especially those which are heavily planted) tend to exceed 5 ppm at night.
For an in-depth discussion of carbon dioxide see Carbon Dioxide (CO2) as well as the graph showing the relationship of CO2 levels to KH and pH.
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Page rev 8.12 of 15DEC98
Originally Posted by cindy
