Water change

What is a pond water change and do you really need to?

A water change is not what you may think, I will explain.

For example, a pond holds 100 litres, each litre has 1g of "impurities" be that chalk, lime etc.

On a sunny day the pond loses 10% of water due to evaporation. You fill it up from a hose and all is well, that's a water change?

No, actually its not, that is a top up.

When the sun evaporated 10% of the water it left behind 100% of impurities, since as they are solids they can not evaporate. So the 90 litres of water now has 100g of impurities, but you also added 10% more water, that will add another 10g of impurities, so now when full the pond will have 110g of impurities.

With a water change you let out 10% of the water, which also means you let out 10% of the impurities, so now the pond is 90% full with only 90% of its impurities.

Again, you fill the pond and yes you are still putting back impurities, but you are only putting back the same amount you took out.

You may want to consider this.

If the above is not true, why does your kettle get "scale" when all you ever do is fill and empty it?

Please note: The numbers and percentages are for representational use only.

POND OWNERS

Quite often you may see or read that if you own a pond you:

"MUST change 10 -20 % of the water volume EVERY WEEK"

I think that, that is a complete waste of time, money and water, I also note, that in the pond industry it is starting to be questioned too.  I believe it comes from the fact that a fish tank usually has no UV, unlike a pond, so with out a UV the water will indeed turn green, but to prevent this you change 10-20% of the water every week, so some assume that if you must do it for a fish tank then you must do it for a pond. Some die-hards say its to do with the nitrate levels, but if the filter is the correct size,  and matured it is not a problem.

Yes if you have dropped in a large dollop of cement then yes, carry out water changes (The lime will affect the water quality) but once your filter is up and running along with a UV, there really is no point in carrying out a water change.

Suppose you have a 1000 gallon pond, that means you have to change 5,200 gallons of water a year, which is not good if like a lot of people are, on a water meter. If you disagree, or have a different view let me know.