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Good Bacteria and Bad Bacteria - What's the Difference?

21st Nov 2019

Anaerobic and aerobic bacteria - what’s the difference?

Bacteria in a pond can be a cause of confusion for most pond keepers, how do we know what is good bacteria and what is bad bacteria? We all know our filter media encourages the growth of bacteria but do we need this in our pond?

The answer is yes, a pond needs bacteria as part of its natural ecosystem to sustain animal life, and without it the water quality would be affected. Bacteria is the background key to any pond’s health, it sits there silently making your life easier, keeping your fish healthy. As long as we are promoting the beneficial kinds of bacteria, that is.

Two kinds of Bacteria

There are two types of bacteria, so let’s start with the bad - Anaerobic. This type of bacteria exists in areas of your pond which have little or no oxygen, anaerobic bacteria can in fact die in areas with oxygen or react negatively – which is one of the reasons we should always ensure we have a good oxygen supply to our pond.

This type of bacteria will break down organic compounds creating sludge in the bottom of your pond which a lot of pond keepers think is a good thing to have as this is where the bacteria lives, however as a by-product of anaerobic bacteria you get Hydrogen Sulphide (the rotten egg smell), this can be lethal to fish in high concentrations and could quickly result in a total pond wipe out! Even in small concentrations Hydrogen Sulphide will cause stress to your fish creating an environment where disease will be much more likely. The table below shows how different amounts of Hydrogen Sulphide can affect your fish.

Now for the good – Aerobic Bacteria. This is the one we need to be promoting the growth of in our ponds. Your filtration system will almost definitely be rich in this bacteria, they help turn lethal ammonia into nitrate (which is plant food). This type of bacteria thrives in oxygen rich conditions, waterfalls, air pumps and fountains are perfect ways of creating the ideal environment for your pond to thrive.

Aerobic bacteria digest organic compounds at a supercharged rate compared to unhealthy anaerobic bacteria’s, therefore providing an air pump straight to your filter is becoming increasingly popular with modern filtration.

So, how can we stop the growth of bad bacteria, and encourage the growth of good bacteria? A starting point to stop the growth of any bad bacteria would be to purchase a pond vacuum to get rid of any harmful sludge in the bottom of your pond, and to encourage the growth of good bacteria make sure your pond is really well aerated using some of the methods we mentioned previously! This is particularly important in the summer months as ponds tend to lack oxygen when the weather is warmer, so make sure you’ve got your air pump ready or fountains set up as we will hopefully start to see some warmer weather sooner rathe