What’s Consuming Oxygen in Your Pond?

What’s Consuming Oxygen in Your Pond?

Carol Mund

After reading a great article titled “Oxygen in Ponds” by Ben Helm of www.watergardenersbible.co.uk, I wanted to share some of the highlights which will encompass several posts.

The ecosystem that is home to our prized koi and other fish has some requirements to keep it balanced.  One such requirement is the Dissolved Oxygen Concentration (DOC).  DOC refers to the amount of oxygen that is dissolved in the pond water, which measures how much oxygen (by weight – mg) is dissolved in every liter of water.

There are many occupants of a pond that affect and rely on the DOC in a pond.  Let’s look at a few of them.


At a macro level, koi aren’t the biggest consumers of oxygen in the pond (but this will vary with stocking density).  And compared to other species of fish, koi are quite tolerant of lower levels of DOC requiring 6 mg per liter.  A trout, however, prefers a higher DOC level of around 12mg/l.

Koi absorb roughly 80% of their oxygen through their gills with the remainder consumed in their lungs.


The majority of bacteria found in ponds (usually found in the filter) require oxygen; thereby we classify them as aerobic bacteria.  Their DOC consumption varies depending water temperature and food content in the pond water.

With the warmer weather brings active fish.  Ammonia levels will be on the rise once fish begin to eat, thus requiring bacteria to become more active to consume and convert ammonia to nitrites, then to nitrates.  This increased bacterial activity will result in more oxygen consumption as well.


The more mature of filter becomes will bring a greater diversity of colonized invertebrate life.  Likewise, these critters will require the use of oxygen as they help to consume the organic matter in the pond.


From microscopic to larger forms, plants consume oxygen just like all the other life forms in the pond.  Plants can also add their excess oxygen, over and above what they need, back into the pond during the day.

In our next post, we’ll look at what factors can cause your DOC to drop.

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