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How to Decide on Pond Depth and How to Determine Average Depth in an Existing Pond

Ask a pond keeper how deep a fish pond should be and you'll get a variety of different answers. Ask a Koi keeper the same question and they'll say at least 6 feet. Few will qualify their answer and so confusion reigns and the wrong type of ponds inevitably get dug that in the end do not suit the person who wanted the pond in the first place.

Let's try to demystify the question of pond depth and then go from this concept to calculating pond volume in a general sense.

As you read below bear in mind some people talk feet and others metres so here are the basic conversion factors: 1 foot = 30.5 cm, and 1 metre = 39.3 cm.

How Deep Should A Garden Fish Pond Really Be? ... Well It Depends

Sure if you want to win first prize for the largest grown Koi at the local annual Koi completion then immediately I will agree 6 feet is a good depth for your pond .... for the reason that high quality, fast growing, well fed Koi need space to exercise and in which they can develop correct body shape. Koi also prefer more stable pond conditions. In deeper ponds temperature swings are far less between day and night and by virtue of the large volume, pollutants if they exist are in low concentration unless a really bad filter problem happens to occur.

But is this what you meant when you said you wanted a koi pond? Probably not ... you were probably referring to having a pond with a variety of those living jewels in it just to enjoy for their colour and pet-like behaviour.

In this case a pond of about 3 or 4 feet depth would certainly be OK ... in fact less would also work. Of course you could expect fairly large swings in temperature but koi in general will tolerate these changes.

Most aquatic plants prefer shallow ponds so if you want a simple water garden with a few fish then ...

A pond between 2 feet and 3 feet is fine. Bear in mind  that deep ponds cost much more than shallow ponds. In the final choice personal preference, space and budget will be decided along with common sense.

The basic principle behind pond volume calculation is getting the average depth right.

At some stage or another (pond treatments, medical dosages etc) you'll need to calculate the pond's volume. The fundamental formula is simple .... the volume of any pond is the surface area multiplied by its average depth. However getting both these numbers correct can be a major challenge for most of us. It's also true that total precision is not really necessary yet the more accurately you know both average depth and surface area the more accurate your calculation of pond volume will be.

If you have a pond and the depth is not constant you can make a very good estimate by taking a stick.

  1. Mark the stick or pole at 1 inch (2.5 cm) intervals using an indelible ink pen.

  2. Insert the stick at 10 different places in the pond covering the general contours of the pond bottom and record each depth, by the time you've finished you'll have 10 numbers.

  3. Add the numbers together and divide by 10.

  4. Use this answer as the average depth of the pond.

Click here for discussion on pond volume calculation


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