Author Topic: Something to think about, on water hardness!  (Read 856 times)

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Something to think about, on water hardness!
« on: April 02, 2010, 08:37:13 AM »
Here is an article on water hardness that should help to explain how the minerals in our water affects our fish.

Water hardness and it's effects on our fish:

Water hardness is, from a fish's viewpoint, one of the most important aspects of water quality as it affects so many areas of fish health. Despite this importance to both fish health and water quality, it is often a poorly understood subject.
Indeed, many fish keepers never check water hardness. This seems particularly true of koi keepers to whom it is especially relevant because of the high levels of nitrification taking place in a well-stocked koi pond.

Water hardness has a major effect on pH and pH stability. It will effect the toxicity of many common substances, including some fish disease treatments. It also has a major effect on fish osmo-regulation, a process you may recall, that is vital to fish health.

So what is water hardness?
As many of you would know, water accumulates many dissolved substances and minerals from it's various sources before it reaches our taps.
Hardness is a measurement of the concentration of divalent metal ions such as:
zinc etc
Usually acquired as the rainwater percolates through rock and filters down into our reservoirs and ground water. In most cases the water around Australia, consists mainly of calcium and magnesium salts, with trace amounts of other metals.

Two types of hardness:
This subject gets a little confusing because there are two types of hardness that we need to keep in mind for our fish keeping. The two types are permanent hardness and alkalinity (often referred to as carbonate or temporary hardness(kH) ). The sum of both types of hardness is called the general or total hardness (gH).

Alkalinity(kH) refers to the hardness derived mainly from carbonate and bicarbonate ions, and directly reflects the ability of the water to buffer back up. This form of hardness is also called carbonate hardness or temporary hardness because it can be removed from our tap water by boiling the water before we use it in our tanks. A good demonstration of how these minerals are removed by the boiling process, is how lime-scale builds up in kettles and showerheads!

Permanent hardness(gH) measures the ions such as nitrates, sulphates, and chlorides etc, that are not removed by boiling. Most of these do not effect your water buffering but can affect pH values.

In most water supplies around Australia, general hardness and alkalinity measurements(as mg/litre) are likely to be very similar, as a lot of Australian water supplies are drawn through limestone, and through desalination plants, as we are a predominately coastle dwelling country, resulting in similar mineral counts in water supplies around the country.

While there is a very close connection between water hardness, and it's ability to buffer back up, it should be made clear that hardness is a product of mainly calcium and magnesium ions. While buffering is produced by bicarbonate and carbonate ions. The fact that the two are so closely related is due to the fact that most hardness around the country is formed from calcium and magnesium carbonates.

So, as a rule of thumb for Australian water, hard water is usually well buffered while soft water is usually less well buffered. However, we should be aware that it is possible in certain places, because of different water composition, to have hard water that is poorly buffered, i.e water where permanent hardness predominates, or soft water that is well buffered, i.e. water that has high levels of sodium or potassium carbonate, rather than calcium or magnesium. Obviously the simple way to establish the makeup of your local tap water, tank water and pond water(they may not be the same), is to test for both types of hardness. Test kits are readily available at all good fishstores for measuring both types of hardness.

The carbon dioxide/ bicarbonate/ carbonate buffering system
The initial pH of water is determined by the type of dissolved compounds that it has accumulated, although it may well be chemically altered by the water company before it reaches your tap. However, once it is in the pond or tank, water pH is also influenced by other factors such as plant and animal respiration, excretion and plant photosynthesis. Without some form of buffering these natural activities would cause huge diurnal swings in pH.

The most common buffering system is the the carbon dioxide/bicarbonate/carbonate buffering system.
Essentially it stabilises pH by mopping up excess hydrogen ions and then releases them again as levels drop, so that the hydrogen concentration, and therefore the pH, stays fairly constant.
CO2 + H 2O H2CO3 HCO - + H + CO32- (solid) + 2H +

What this equation tells us (from left to right) is that carbon dioxide, excreted by fish and plants, dissolves in water to form carbonic acid (H2CO). If pH levels increase, that is the water becomes more alkaline (say from plant photosynthesis), then the carbonic acid dissociates to form bicarbonate and hydrogen ions (HCO3- + H+). Hydrogen ions are acidic-forming ions and will therefore counteract the alkalinity increase. If the pH continues to increase, the bicarbonate will dissociate to form solid carbonate and release yet more hydrogen ions (CO32- (solid) + 2H+), to counteract the increased alkalinity. The solid carbonate is the chalk layer covering the pond bottom and walls (or the kitchen kettle). If pH levels start to fall the process is reversed. At a normal pond pH of 7-8 some of all of the above species will be present, with bicarbonate dominating. Carbonate will predominate at pH's above pH 9.

The buffering capacity of you water depends on the total amount of bicarbonate and carbonate present.
Water that has low levels of these ions will quickly exhaust its ability to counteract pH fluctuations.

Fish health and water hardness:
Different species of fish have varied water hardness requirements, so it is important to find out what hardness is best for your fish.

Water hardness effects fish health because it influences osmoregulation. Being open systems, fish are affected by the makeup of the surrounding water. As a consequence of osmosis, freshwater fish are subject to a continuous influx of water, while marine fish have to live with a continuous outflow of water.

Against this continuous movement of water into or out of the body, fish have to maintain a constant internal body fluid concentration – a process called osmoregulation. The greater the difference in concentration between the fish's body fluids and the surrounding water – the greater the osmotic effect. As hard water is more concentrated than soft, there will be less difference and therefore less water influx and consequently the fish will not have to work so hard at osmoregulation. This is particularly important in cases of bacterial ulceration where water can flood into open tissues.

Water hardness and disease treatments:
Some common fish disease treatments are affected by water hardness, and therefore needs to be considered when calculating dosages. Probably the most sensitive is chloramine-T, which is quite toxic in soft, acidic water.

How do I change water hardness?
First because nitrification is continually removing alkalinity it is important that hardness is monitored on a regular basis – say about once a month. If either alkalinity or general hardness falls below the optimum level it can be reversed by either adding a calciferous source such as crushed oyster shell to the filter or adding more buffer to the water. If alkalinity is too low then add a carbonate buffer. If general hardness is too low then add a calcium or magnesium buffer.

Hope this helps to give some background knowledge about our water hardness and how it effects our fish. ;D