Hardness of your pond water and impact upon pH

I have heard from two readers very recently who decided to make adjustments to their pond water based upon pH measurements they made ... on this basis I thought let me go into this matter of pH more carefully and in a sense this is therefore a continuation of the previous pH problem article special edition ...

NOTE THIS VERY CAREFULLY ... pH is an extremely complex pond variable.

It is almost impossible to make an accurate adjustment even in the unlikely event you have measured the result correctly and you have taken the sample at the right time of day. So why measure it? .. well as I suggested before; don't unless you must and only then use the result to compare to historical trend results. There are mathematical reasons and chemical reasons for this difficulty in measuring pH ... the maths problem is due to logarithmic variability and not simple proportional or linear variability but we are already getting too complicated.

The chemical reason is the result of what is called "buffering" and that is what we will talk about. Buffering is better understood by talking about hard and soft water which are terms most of us are familiar with.

Briefly buffering does what the word describes ... it buffers, insulates, minimizes, or protects against excessive pH variations in pond water due to changing acid or alkali content so that pH does not necessarily change too much when more acid or alkali is added to water. Pond water low in buffering capacity therefore can show large swings in pH when acid or alkali is added or even depending what time of day it is.

In general buffered water (hard water) is normally better for pond inhabitants ... more in a moment but lets talk a bit about fish stress first.

Fish become stressed when their living environment (the pond water) changes significantly ... hence the recommended procedure for introducing new fish to pond water you will all be familiar with I am sure ... i.e. let the temperature between the bag water and the pond water slowly equalize by floating the bag on the pond and/or by adding small amounts of pond water to the bag before releasing the fish.

Trying to make changes to water pH by adding chemicals of any kind introduces stress. When fish are stressed they become prone to disease from lurking bacteria which are always present in your pond water. So do not create stress situations and you will lessen chances of bacterial disease problems. Large daily pH fluctuations also create stress.

HARD WATER ... what is it? learn a lot more here

The easy way to recognize if general hardness exists in your house is by washing your hands and face ... if it is difficult make a lather and if a scum is left around the basin or bathtub then your water is hard. If your, skin, hair and laundry is less bright than you would like it then you may have a case of hard water. If lather forms easily and there is a slimy feeling to the water then the water is soft.

Of course you can measure hardness and this is probably one of those tests worth doing on pond water now and again... . but if you measure it make sure you understand the result before making any adjustments.

 In gold fish ponds it is really unnecessary whereas with prize koi then it is worth doing with a high quality test kit.

When you measure hardness you are actually identifying the amounts of calcium and magnesium hydroxides, carbonates and bicarbonates in the water .. also called temporary hardness (because such hardness can be removed by boiling water which releases carbon dioxide and leaves insoluble calcium carbonate behind ... see the scale inside your kettle). By changing to a different test kit you can measure other types of hardness such as sulphates and chlorides ... referred to as permanent hardness.

Total hardness is the sum of both types of hardness.

In general it is good to have harder water (hard due to carbonates) in your pond because it assists greatly in controlling variations in pH and also prevents metallic impurities (such as copper which then becomes insoluble) becoming a significant problem for your fish. In addition hard water helps a fish to regulate its own metabolic processes and reduce stress somewhat. Hard water is normally on the alkaline side of pH ... i.e. more than 7

To try and give you a feel for how much pH can vary in a planted pond or one with algae growth (source of carbon dioxide during night) consider the following general statement ...

If pond water just before darkness falls has a pH of 8 and a low hardness of say 0.3 and carbon dioxide released by plants or algae amounts to say 5 units overnight then the pH at dawn might be as low as 6.8 because the released carbon dioxide is naturally acidic. Now if the same water with a pH of 8 had a hardness of about 2.0 then by dawn the pH would have fallen to only 7.5 due to the same amount of carbon dioxide being released. The hardness has "buffered" the water from excessive pH fall.

This process reverses itself during the daylight hours.

So you can see large swings in pH result from low hardness values.

Yes water can also be too hard and this situation assists in the formation of string algae or blanket weed which is a curse. In very hard water pond keepers get excessive algae build up on the sides of ponds).

Softening hard water where you have string algae problems can help. You soften hard water by mixing soft water ... e.g. from a home water softener unit (see Pond Professors pages on this subject here) which many homes have.

Water hardness can be improved by adding sodium bicarbonate and I have seen it suggested that the best material is calcified seaweed ... here's a description I found on the web ...

Calcified Seaweed is a calcareous marine algae resembling coral, known to marine biologists as Lithothalium Calcareum. It is dredged from the seabed mainly off the Brittany coast, dried at low temperature and crushed to a fine powder, which is readily assimilated by the soil. It contains about 46% calcium oxide, 5% magnesium oxide; sulphur, copper, iodine and cobalt and some twenty trace elements. It is an ideal soil conditioner and clay breaker and can be used on lawns, beds and borders as an alternative to 'lime' to correct soil acidity. It is highly favored by chrysanthemum, sweet pea, dahlia, leek and onion growers. It is non-toxic and safe to use does not scorch and stores well if kept in a reasonably dry place.