Saturday, 14 April 2012

Do You Really Know The Volume of Your Pond?

 

Why Do We Need To Know The Volume Of Our Ponds?


The importance of knowing the accurate volume of your pond is often overlooked. How often do you hear people saying that their pond is “about” 3,000 gallons, 20,000 litres or whatever it might be – but how accurate is “about”?  

A 10ft x 10ft x 4ft 6” deep pond (approx 3m x 3m x 1.5m) pond has a volume of approximately 2,800 gallons – assuming the walls are vertical, the base is flat and we ignore the filters and pipework. A simple 6” (150mm) change in the water level will result in a difference of +/- over 300 gallons (that’s more than 10%). It’s easy to see that, by the time we have benched the bottom of our ponds, added some filters and pipework or built an irregular shaped pond, our estimates can be quite a way out. At best, this will result in under-dosing of our ponds that will mean treatments are ineffective - but is potentially fatal if we overdose our ponds!

By far the easiest way to measure the volume accurately is to use a water meter when we first fill our pond and filter systems. However, if your pond has already been filled and you don’t know the accurate volume, all is not lost – it is possible to determine the volume very accurately, by measuring the salinity of you pond!

The Simple Science of Water Salinity.


It's much easier to explain and measure water salinity using metric figures. If you prefer to know the volume in gallons, it’s still easier to do the measuring in metric and simply convert the final figure to gallons. Just remember that: 
1 tonne of water = 1000 Kg = 1000 Litres = 220 gallons
1 litre of water = weighs 1Kg - or 0.1% of a tonne.

Spookily, 1Kg salt is also equal to 0.1% of a tonne. Therefore, for every 1Kg salt you add to 1 tonne (or 1000 litres) water, you will raise the salinity by 0.1%. Similarly, if you add 10Kg salt to a 10 tonne pond (10,000 litre pond), it will increase the salinity by 0.1%. 
So, for the same 10 tonne pond (assuming the present salinity is 0.0%) to increase the salinity to 0.3% (a good “tonic” level) you will need to add 30Kg salt.

Here's How To Work Out The Volume Of Your Pond By Measuring The Salinity. 

Calculating the volume of your pond (including filters and pipework) using the salinity method is simple - providing you have a salt meter and some accurate scales. All we need to know is:
  • The amount of salt we add (in Kg), and
  • The increase in salinity after we've added the salt.
  1. Measure the salinity of your pond without any salt added and record the figure. (Let's say 0.01%)
  2. Weigh the salt accurately (e.g. 30Kg). Remember to use pure vacuum dried salt (PVD).
  3. Dilute it in a bucket a few Kg at a time and add each bucket to the pond until all the salt has been added - this will prevent any salt burns to your koi.
  4. Allow about 24 hours for the salt to distribute evenly throughout the volume of the pond.
  5. Take a second salinity reading (Let's say its 0.31%)
  6. Subtract the first salinity reading from the second reading (a nice neat 0.3% in this example) - this is the figure you use in the calculation.
Now:
  • Divide the amount of salt in Kg by the increased in salinity
i.e. 30 divided by 0.3 = 100
  • Multiply this figure by 100
i.e. 100  x 100 = 10,000

This is the volume of your pond in LITRES.
If you really want to mess about with gallons - just divide it by 1000 (to get tonnes) and then multiply it by 220.
E.g. 10000 / 1000 =  10 tonnes.  10 x 220 = 2,200 gallons in this example.

Some Words of Warning!

Whilst many koi keepers advocate the use of salt for treating koi and aiding recovery, it must be remembered that koi are fresh water fish and should not be kept in salt water for long periods.

It can also be very difficult to remove all the salt from a pond without doing a complete water change. A 50% water change will only remove 50% of the salt. A further 50% water change at a later date will only remove 50% of the salt that remained after the original water change, i.e. 25% of the salt will still be in the pond even after 2 water changes of 50% each time. A further two 50% water changes (meaning you’ve changed the total volume of your pond twice) will still leave 6.25% of the original salt in your pond!It is therefore essential that you accept that several large water changes will be required after using salt in your pond.

Finally, great care should also be taken when treating a previously salted pond with Formalin or any treatments containing Formalin.

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