There will certainly be a lot of differing opinions on the best water conditions for koi but one thing remains constant: poor water quality leads to a host of other health problems that are certainly avoidable with proper care. Because stress originates from poor water quality, follow these guidelines for healthy water and healthy koi.
Oxygen levels should be at a minimum of 5.0 mg/L for koi. In the fish world, there is some variation with the tolerable level of dissolved oxygen in the water but 5.0 is a good baseline. As a reference, 5.0 is the minimum for koi and 18 mg/L is the physical maximum that water can hold. Just as a reminder though, cold water can hold more dissolved oxygen than warmer water so higher summer temperatures (and overcrowded ponds) will lead to lower dissolved oxygen, which is really when you will want to pay attention to it the most. Oxygen becomes dissolved into your koi pond in several ways. At the very surface there is limited diffusion occurring between the atmosphere and the water and that accounts for only a small amount of dissolved oxygen. Turbulence will also agitate the water enough to generate dissolved oxygen in your pond and this often comes in the form of falling water as from a small water fall. A tried and true and popular way to increase the dissolved oxygen in a koi pond is by an air stone on the bottom of the pond or by spout or fountain shooting water up into the air.
Okay, back to chemistry class everyone because its time to discuss pH. As you may recall pH has something to do with acids. Its all about acidity and alkalinity. The pH scale is a logarithmic one meaning when your pond jumps from 7 (neutral) to 6, its not simply getting a little bit more acidic, its getting 10 times more acidic. Conversely, when your pond tests at 7.5 and then gets increasingly alkaline by jumping to 9.5, then your pond just got 100 times more alkaline (10 times 10). So it’s a big deal when your pH changes and can definitely affect your koi in negative ways. pH, or power of Hydrogen, should range in your pond somewhere between 6.8 and 8.2 but do your best to keep it as stable as possible.
Ammonia, Nitrites, Nitrates
As you may recall, the general cycle of waste in your pond starts with ammonia excreted by your fish then bacteria and oxygen break it down to nitrites which later get broken into nitrates then free nitrogen. Ammonia, nitrites and nitrates all have the ability to cause health problems for your koi if their levels are not kept in check. Along with other health problems, ammonia can essentially burn your fish’s gills and reduce its ability to extract dissolved oxygen from the water. High nitrites can damage your koi’s kidneys and nervous system and high nitrates, for extended periods, can cause your fish’s immune system to be compromised. Ammonia and nitrites and the most troublesome when it comes to health problems for your koi but don’t underestimate the power of nitrates over long periods of time. Here is a guideline for these three water chemistry measurements.
-ammonia: levels should be zero. Depending on your pH, you can get away with 0.5ppm (parts per million) or 1 ppm for a short period of time but keep in mind that above a pH of 8.0 ammonia becomes more toxic.
-nitrites should be less than 0.25 ppm but ideally you should have a reading of zero.
-nitrates: a reading of 20 to 60 ppm is acceptable.
The use of salt in koi ponds has, for long time, been a tried and true method to deal with various water quality and health problems that arise. Some of the benefits of salt is that its a cheap way to keep some disease at bay, control algae and may also lower nitrite toxicity. Additionally, salt plays a part in the osmotic pressure between the fish and the outside aquatic environment. There is a differential between the solute concentration of the fish’s blood and the fresh water that it swims in so the addition of salt actually lowers that concentration differential and makes it easier on the fish by reducing the amount of work its body has to do. A salinity of up to 5 ppt (parts per thousand) or 0.5 % is acceptable.
Temperature obviously plays a big role in the overall health of your pond and it warrants your attention. Temperature can exacerbate existing problems, especially higher temperatures. For example, warmer water holds less dissolved oxygen and ammonia can be more toxic. Although koi can handle temperatures of between 35 and 85 F degrees its best to keep your fish in water that ranges between 65 and 75 F degrees. And as with pH, try to avoid large temperature swings.