Nitrite (part 1)

Nitrite (NO2-) is formed from ammonia in the biological filter. This is part of the nitrification process, which is described in general terms in a previous article From this series. When nitrite levels in the pond rise too high, its inhabitants can get into trouble. A nitrite level of 0.2 milligrams per liter of water is harmful to your fish. That's only one part in five million! It's therefore important to keep the nitrite level in the pond below 0.2 milligrams per liter. Of course, it's important to monitor your pond water for excessive nitrite levels. Testing is and remains very important.

How is nitrite formed?

Nitrite is created when specific nitrifying bacteria convert ammonia (NH3 + NH4+) into nitrite (NO2-). To facilitate this process, we need to create several preconditions in the pond:

The biological filter must have sufficient surface area for the necessary bacteria to grow. Nitrifying bacteria hardly float freely in the water, but settle in a thin film on all surfaces in the pond and filter. Since we usually keep many fish in our ponds on a small amount of water, there is often insufficient surface area in the pond by nature, and therefore we need a organic filter needed to increase this surface area.
The process of converting ammonia into nitrite uses a lot of oxygen (O2). We will therefore have to do this, especially in warm weather. aerate to supply the pond with sufficient oxygen.
To provide the biological filter with a sufficient supply of pond water, we ideally need to pump the pond's contents through the filter within two hours. Even better is once an hour.
The pH should be between 7.0 and 8.5, and the KH ideally between 4 and 9 degrees DH. ( Pond test kit )
Nitrifying bacteria don't like light, so cover the filter.
There must be nutrients present in the form of ammonia. This is released naturally when you feed the fish.

The danger of too high a nitrite value.

When nitrite levels in the pond become too high, the fish can suffocate. Nitrite has the unpleasant habit of binding to the red blood cells in the fish's bloodstream. This prevents these red blood cells from performing their function of transporting oxygen from the gills to the fish's organs and muscles.

Characteristics of a nitrite peak.

With a nitrite spike you can expect the following symptoms:

Listlessness of the fish due to a lack of oxygen in the body (there is not necessarily also a lack of oxygen in the water).
Rapid breathing.
The “hanging” of the fish just below the water surface or at the outflow of a filter or air pump, because that is where the water is most rich in oxygen.
Brown, instead of bright red, gills.
Decreased or complete loss of appetite.
Weakening of the fish, reduced resistance and more susceptible to secondary diseases.

In part 2 we will look at how we can prevent a nitrite peak and what we can do if a peak does occur.