Reducing nitrite using salt

Balancing ammonia, nitrite and nitrate can be an ongoing issue, but with a pinch of salt and a heap of advice from Mark and Lisa Davis stirred into the mixture, the nitrite nightmare can be resolved…

The subject of nitrite and its effects in Koi ponds can become very technical in explanation, but it is very important that as a Koi keeper, you understand the implications of its presence. If the nitrite level in your pond is too high, it can be detrimental to the health of your Koi. For this reason, we will try and explain the presence of nitrite in a way that everybody can understand and only stick to the basics and the most necessary information.

Water balance
After the Koi in your pond have digested their food, they excrete the waste into the water, and the most harmful portion of this is released as ammonia. The ammonia passes into the filter where bacteria grow and these bacteria (Nitrosomas) use the ammonia as a food source. The Nitrosomas bacteria then excrete nitrite as a by-product and, at high levels, nitrite is toxic to Koi. Fortunately, another group of bacteria in your filter (Nitrobacter) eat the nitrite and they convert it into nitrate, which is a lot less toxic. There is also yet another group of bacteria that break down the nitrate into free ammonia, or nitrogen gas, which is released into the atmosphere when the surface of the water comes into contact with air. Therefore, the more you feed your fish, the more ammonia is released, and the more ammonia that is released, the more the Nitrosomas bacteria have to eat. The Nitrosomas bacteria then grow faster and reproduce, so more nitrite is released.

Nitrite levels can build up if, for example, a lot of ammonia is suddenly being produced, perhaps due to overfeeding or the introduction of a large number of new fish to a pond, that are then being fed. The colony of bacteria in the filter that have developed to cope with the existing levels of ammonia and nitrite suddenly can’t cope with the increased levels and so the ammonia and nitrite rise and become toxic to Koi.

During the cold winter months, the bacteria in the filter die back and when spring comes along and the water warms up, it can take a few weeks for the bacteria colony to be completely effective – this is the time to slowly build up the amounts that you feed your Koi and not go mad by giving them too much food when they suddenly become ravenous.

High nitrite effects
Nitrite levels over 0.15mgl can be damaging to Koi and high levels of nitrite can result in something called brown blood disease, which prevents the transport of oxygen into the blood and results in a fish suffocating, despite there being sufficient levels of oxygen.
Signs that fish are suffering from the effects of high nitrite levels or nitrite poisoning are that they might rub themselves (flash) on the bottom of the pond or lay with fins clamped to their sides on the floor of the pond – but still come up for food only to return afterwards to the pond floor. When nitrite poisoning is advanced, a fish will be gasping for air at the surface and eventually die.
In an emergency, nitrite toxicity can be reduced by adding salt to the pond (which puts chloride ions into the water) and maintaining a level of salt concentration of 0.3% in the water will usually alleviate the effects of moderate-to-high levels of nitrite. Also, stop feeding for a few days and carry out a partial water change before adding salt. Sudden rises in nitrite levels can be prevented by feeding a consistently even volume of food on a regular basis, so that you don’t get sudden fluctuations in ammonia production. Good filter maintenance and avoiding chemical and environmental shocks can also prevent rises. Regular water changes of 10% per week, and good filter and pond maintenance, are not just good for the health of your Koi, they are also good for the health of your filter. Whatever filter media you use, make sure that you clean it weekly and if you have to wash the media, use water from your pond and not from your tap as chlorine in tap water will kill filter bacteria.

Chemical shocks can be the result of a medication that has been used to treat your fish, or chemicals such as potassium permanganate or Formalin. This will not only kill parasites but also kill off some of the bacteria in the filter.

If you do have to shock your filter system with a chemical to treat a parasitic infection in
your pond, then it is important to slow down your feeding rate and then increase it gradually over a period of a week or so, so that your filter can build up a healthy population of bacteria once again.

Managing your pond
Until a filtration system is completely and fully mature, the ammonia and nitrite levels will peak and trough. These fluctuations can take place at different times throughout the course of a day, so just because you have a slightly high nitrite reading at one particular point in the day, it doesn’t mean that you necessarily have a problem – it could be that the bacteria that eat the nitrite (Nitrobacter) haven’t yet multiplied into a population that can digest all the nitrite that is being released. However, it will only take a short time for that population to react to the increase in nitrite and, with careful feeding, you can build up a healthy population within a few weeks without any detrimental effect on your Koi.
The rise in the population of bacteria in a filter is totally temperature and environment dependent and oxygen plays a major part, too, because the bacteria in your filter (Nitrosomas and Nitrobacter) are oxygen-breathing. Biological filtration is an oxygen using process and a sufficient amount should be provided not just for your Koi but also for the filter bacteria.

Salting the nitrite
It should never be your aim to get your pond water to have zero ammonia, nitrite or nitrate because the bacteria in your filtration system would never have anything to eat and would starve. If this happened, your filter would stop working – fish inevitably need to eat and will inevitably excrete ammonia, so it is an unrealistic aim to have readings of zero. If, however, you feel the levels of nitrite are getting too high and are not showing any signs of reducing, or are at levels that you feel are toxic to your fish, then the immediate addition of salt will help reduce the toxicity of the nitrite.

Salt works because it increases the levels of chloride ions in the water and, at concentrations of 0.3%, there are enough chloride ions in the water to block the nitrite molecules and stop them from diffusing into the Koi – it won’t stop all of them though, so this is only a temporary measure.

We recommend that you use PDV (Pure Vacuum Dried) salt. The salt mustn’t simply be dumped into the pond – it must be dissolved before it goes in. We add a large amount of salt to a bowl, fill the bowl with pond water, give it a good stir, let the solution settle and pour off the dissolved salt solution into the pond water. When we worked for a time in Germany, we found salt tablets were used and were suspended at the side of the pond in a net bag so that the fish had no way of coming into direct contact with high salt concentrations.

Table salt contains iodine and is toxic to fish, as are salts with arsenic-based, anticaking agents, so you must be very careful when choosing which salt to use. Your local Koi shop should stock the correct type.

Salt, like any chemical, must only be used as a last resort and I would highly recommend that when you do use it, you use a salt test meter to check that the dosage is correct and between 1kg to 6kg of salt per m3 (or 220 gallons) of water. If you haven’t got an electronic salt meter, there are alternative tests available from marine aquarium shops, or you can even use a hydrometer. The meter should read between 0.1% and 0.6%. Koi can survive higher concentrations of salt for a reasonable length of time but I wouldn’t recommend levels above this for inexperienced Koi keepers.

Adding salt has an immediate effect on the nitrite levels – if you add too much salt to the pond, you must quickly try and rectify the problem and bring the level down to below 0.7% as fast as you can by doing water changes. Or in drastic situations, take the fish out and put them into fresh water.

Alternative methods
You can add commercial cultures of Nitrobacter to your filter to help boost the population of nitrite-eating bacteria, and reduce nitrite levels more quickly. However, these are expensive and some are useless, as Nitrobacter are oxygen-breathing and they won’t be effective unless they are supplied in an oxygenated environment. The other way to reduce nitrite is to add zeolite – a mineral that absorbs ammonia and, as a consequence, leads to a reduction in the amount of nitrite. However, you shouldn’t use zeolite and salt at the same time, as salt will have the effect of releasing the ammonia stored in the zeolite.

Salt must only be used, like any chemical, as a last resort. Levels must be monitored and controlled to ensure the desired level of concentrations is provided.

As soon as any problem has been alleviated, the salt concentrations should be brought back to normal as soon as possible by carrying out water changes.