Chapter 3 Variations in Water Supplies
Readers can be forgiven for believing that all water from household taps is the same. One of the few similarities is that it is wet and relatively inert and pure enough for drinking purposes. Depending upon where you live, the water from your taps may be “hard” or “soft”.
Why do different areas have differing water supply types?
When rain falls from clouds it is pure water – H2O. As it falls towards land it is exposed to gases in the atmosphere – typically carbon dioxide (CO2) and sulphur dioxide (SO2).
Rainwater readily absorbs these gases and once in solution the rain becomes a weak acid. We have all heard of “acid rain” which is caused by the burning of fossil fuels such as coal and oil.
If the rain falls onto land which consists of hard granite or sandstone, the weak acid dissolves little of the rock and it collects in reservoirs as “soft” water.
If it falls onto land, which consists of limestone, usually magnesium limestone also known as “dolomite”, which contains calcium and magnesium carbonate, the water quite readily dissolves these rocks and water collects in reservoirs as “hard water.
This water will contain a range of dissolved trace minerals from the rocks and soil, mainly calcium and magnesium which are primarily responsible for the “hardness” of the water, together with bicarbonates which provide the alkalinity (K.H).
Generally speaking and contrary to many beliefs, this water is preferable for koi keeping in filtered ponds as it contains good quantities of calcium and magnesium, buffering agents (alkalinity) which counter the natural processes which are tending to make the water more acidic and drive down the pH of the water.
Know the water you have available to work with.
The pH of the water is usually, but not always, an indication of its “hardness”.
It is quite important that all koi keepers know about the water they have available to them. A pH of 7.4 is considered by some as ideal for koi ponds, however filter bacteria prefer a pH of 8.1 and an alkalinity (K.H.) between 100 and 150 ppm to operate at there maximum efficiency. Always remembering that we are relying upon the filter bacteria to process the ammonia which is continually being produced by the koi, and bearing in mind that we are water keepers first and koi keepers thereafter, it would seem wise to accommodate those organisms which help to prevent the deterioration of the water to levels which would prevent successful koi keeping.
Taking a reading of the pH straight from the supply tap can give false readings because our drinking water supplies often have their pH values modified so that they do not interact with the metal network pipes and fittings. This can be experienced mainly in “soft” water areas where the natural pH of the water is below pH 7 but is raised above 7.0 to reduce the corrosion to pipes within the system. The chlorine based disinfectants used, both increase the pH and sterilise the water making it suitable for drinking purposes. I have seen water from a tap in such a soft water area be 9.6 simply due to the over use of chlorine by the water authority.
In areas where water is classed as hard it is often obtained from wells or boreholes. Water from these sources frequently contain large amounts of carbon dioxide; taking a sample direct from the tap of such a supply may give a pH in the region of the ideal 7.4 however once the water is exposed to the atmosphere the carbon dioxide leaves the water and the pH rises. In areas where water supplies emanate from wells or boreholes the pH can rise substantially during aeration as the carbon dioxide which these waters usually contain is gassed off.
My private water supply comes from a borehole at pH 7.4 but rises to 8.1 in the ponds which are strongly aerated.
Water with a high pH does not necessarily mean that it is hard water. Certain waters are high in alkalinity but low in dissolved calcium and magnesium. The alkalinity and pH of soft water can be increased by the addition of sodium bicarbonate. The upper limit for pH when alkalinity is increased by sodium bicarbonate is 8.4
Table of hardness values and classifications.
Mg/litre CaCO3 dH Considered as
0-50 3 soft
50-100 3-6 moderately soft
100-200 6-12 slightly hard
200-300 12-18 moderately hard
300-450 18-25 hard
over 450 over 25 very hard
0.5 Kg of sodium bicarbonate added per 1000 imperial gallons increases the alkalinity by approximately 72 ppm (4 dH).
Water Hardness – The Science for Koi ponds
Water Hardness is concerned only with part of the total dissolved salt content of a water sample. It is a measure of certain metallic ions present in the water and is designated Total Hardness (T.H.).
Calcium (Ca++) and Magnesium (Mg++) both of which are essential to aquatic life are mainly responsible for water hardness; barium, strontium, iron, copper, zinc and other metallic ions also contribute to water hardness too, but are usually present in very small quantities.
The Calcium and Magnesium ions are generally present in three main forms; carbonates, bicarbonates and hydroxides together with smaller quantities of sulphates, chlorides, silicates, phosphates and borates.
The Total Hardness value refers to the total content of all of these combinations of divalent salts and can be sub divided into temporary hardness (also known as carbonate hardness and designated K.H.) which can be removed when a sample of water is boiled and permanent hardness which remains in solution after boiling.
The carbonate hardness mainly consists of Calcium and Magnesium bicarbonates (K.H.); this usually forms the major portion of the Total Hardness.
T.H. = Temporary (Carbonate Hardness) + Permanent Hardness
Testing water hardness in fish ponds and supply water.
Although other metallic ions also contribute to water hardness the major components of hardness are derived from Calcium and Magnesium and most test kits available for testing pond water parameters only measure the amount of these metallic ions in the water sample.
The G.H. test kit measures the total amount of Calcium and Magnesium ions in a water sample. This is sufficient for practical purposes to determine the relative hardness of a water sample for fish keeping purposes.
The G.H. test kit measures the total amount of Calcium and Magnesium ions in a water sample irrespective of whether they exist as temporary or permanent hardness.
The G.H. test kit only measures the main components of water hardness i.e. that contributed by Calcium and Magnesium in its various forms and as stated earlier this is a practical measurement which allows fish keepers a comparative measure of their water hardness.
Two test kits are generally used for testing water in fishkeeping circles; the G.H. test kit has been explained above.
The other test kit used is known as the K.H. test kit and one would immediately think that this would test the Carbonate hardness of the water but it does not actually measure the Carbonate hardness, it measures the ability of the water to resist a change in pH.
The KH test kit measures the ability of a water sample to resist a change in pH; it measures all the alkali (not just those associated Calcium and Magnesium) in the water sample and this is expressed in equivalent mg/lts of CaCO3.
The significance of water hardness
The K.H. test kit provides very valuable information to fish keepers especially those keeping fish in recirculated and filtered systems which use biological filtration. In these systems both fish and the bacteria which process the waste products of fish and of their metabolism, produce significant quantities of carbon dioxide. Carbon dioxide dissolves in water to become carbonic acid and this tends to lower the pH of the water in which the fish and bacteria live. The alkaline components (Alkalinity) of the water sample resist the change in pH that the carbonic acid is tending to produce. Water with a high K.H. value will also resist the affects of other acids in the water such as those introduced by rainwater and other biological processes.
In practical terms the K.H. test kit is measuring the alkalinity of a water sample and it is expressed as mg/lt of Calcium Carbonate, which is what effect an equivalent amount of calcium bicarbonate would confer on the water being tested.
The term “buffer” is sometimes used; this refers to the components of water or to materials added to the water system which resist a change in pH. Usually a buffer resists a downward change in pH by countering the acids being produced in the pond, but a buffer can also reduce the pH and counter the effects of a high pH which is sometimes caused by photosynthesis. Oyster shells, calcified seaweed (Lithaqua) and sodium bicarbonate contain calcium carbonate and are all types of buffers.
Water + carbon dioxide = carbonic acid
H2O + CO2 = H2CO3
When this carbonic acid (H2CO3) comes into contact with calcium carbonate (oyster shell/ CaCO3) a further reaction takes place;
Carbonic acid + Calcium carbonate = Calcium bicarbonate = KH
H2CO3 + CaCO3 = Ca (HCO3)2 or K.H!
Confusion can arise when water is buffered by adding sodium bicarbonate to a pond system to increase the K.H. Although sodium does not contribute to water hardness the bicarbonate provides alkalinity and this is detected as an increased reading by the K.H. test kit but the G.H. test kit will not register any increase in General Hardness.
The G.H. test kit lets us know the actual hardness of the water but only with respect to Calcium and Magnesium. As the other metallic ions are usually only present at trace levels the reading is sufficiently accurate for the practical purpose of fish keeping.
Calcium is needed for koi coloration and health; the required content of calcium in fish blood matches the calcium content of pond water when the water measures 250 ppm GH level. Both calcium and magnesium are needed for bone and scale formation, meaning they are essential to koi coloration. The recommended GH for koi keeping is a range of 80 to 150 ppm. Values below 60 ppm sometimes lead to loss of colour in koi, and values below 40 ppm usually lead to coloration loss, with the coloration loss increasing with decreasing GH, indicating that is highly dependent on the availability of calcium and magnesium in pond water or in the diet of the koi.
Hard water reduces the toxic effects of certain metals in the water such as copper and zinc.
Hard water increases the toxicity of ammonia because of its alkalinity which generally has a high pH
Water hardness influences fresh water fish in terms of osmoregulation; since hard water has a higher concentration of salts than soft water, the osmotic difference between the fish’s internal fluids and the surrounding water is smaller, therefore the osmoregulatory system has reduced work in replacing salts lost from the blood.
The presence of calcium in the water also decreases the cell permeability which reduces the loss of salts and water ingress especially via the gills.
Fish living in soft water need to have more efficient osmoregulatory systems, and they expend more energy to maintain their internal salt/water balance.
Water hardness also effects the regulation of blood calcium levels which also depends upon diet.
Hardwater fish cope with excess blood calcium using an efficient system for excreting calcium.
Softwater fish need to obtain more calcium from their diet and also use bones as calcium reservoirs to ensure that the blood calcium levels remain constant.
Koi are kept in a variety of waters which range from soft to hard, but there is no difference indicated in the food we feed to them with respect to calcium. Koikeepers are in control of the koi’s diet but few consider increasing the calcium levels (G.H.) in their water or in the type of food offered.
I have seen instances where koi with scale and skin damage has refused to heal in soft water but the damage has repaired quickly once the koi were moved to hard water and having seen this, my interest in water hardness was kindled and it has raised questions about the soft water conditions that are often recommended for koi. Soft water usually contains less alkalinity and this valuable component of water is essential in ponds which rely upon biological filtration as previously stated.
Other considerations with water supplies.
All water supplies will contain disinfectants such as chlorine mentioned above. Other substances such as phosphates are sometimes added to improve certain aspects of the water with respect to drinking quality, and metals such as copper, which is extremely toxic to aquatic life, may be dissolved into the water via supply pipes.
Test kits are available for these substances; phosphate levels above 5 ppm can encourage algae problems in ponds and copper levels above 6-15 ppb are undesirable for aquatic life forms.
Test kits are also available for monitoring the chlorine levels in the incoming water supply.