Hard water & pond water alkalinity in koi or garden fish ponds
Water used in ponds should have a degree of hardness which creates a buffering effect and reduces pH variations ... see table below for "definitions" of hardness
However if water is too hard or too soft it can certainly impact upon the aquatic life in any garden pond.
In a pond environment Alkalinity is a more normal term that is closely associated with water hardness.
Alkalinity is a measure of the concentration of alkaline materials in the pond water and the capacity of the water to accept any acidification withour impacting upon the pH too much (this is called buffering capacity and is important to have in well maintained ponds).
Alkalinity is usually measured as either mg/l (milligrams per litre) CaCO3 (Calcium Carbonate) -- see table below.
The ideal range of alkalinity for pond fish is 20 - 300mg/l. If alkalinity is below 20mg/l the water will be extremely soft and will have a very low buffering capability and thus pH will vary a great deal.
Any acids finding their way into the water into the water (for example after heavy rain which is on acidic side), will cause a big fall in pH.
Such fluctuations of pH are harmful to fish since all fish prefer stable and non-stressful situations. Water with low alkalinity can be treated with lime ... many pond keepers place shells inside filters to increase alkalinity. High alkalinity levels can sometimes lead to a condition in the fish called nephrocalcinosis (high calcium concentrations in kidneys)
Hard water that is too hard is best reduced by mixing in softened water ... and this can be achieved using the in-house water softener.
What is hard water? Hard water contains calcium and magnesium and this is quite natural. However excessive amounts create what is commonly referred to as hard water. High levels of hardness occur in water that occurs in chalky countryside, in areas where limestone is present. In England some rivers are referred to as chalk streams ... rivers that are not greatly effected by rain and tend to flow nice and smoothly. The water feeding these streams is rainwater that percolates through calcium and magnesium rich structures.
Hard water tends to support lots of river life and trout grow big. In the USA chalk streams are often called Spring Creeks.
Most natural water supplies range contain from around 3 grains per gallon (gpg) to 50 gpg (or 51 mg/l to 855 mg/l). These hard water substances precipitate and leave a film or scale on surfaces that come in contact with the water ... like the bath tub, coffee cup and so on.
The easy way to recognize hard water
Hard water in the hole will form lime scaling in pipes, water heaters, boilers, and air conditioning systems. The impact of this is higher fuel bills and often permanent damage to pipes and heating equipment. In water heaters scale even in minor thicknesses can reduce a water heater's efficiency by up to 15%. The scale acts as an insulating material and thus lowers the rate of heat conductivity.
In very hard water it is difficult to make a lather when washing and soap consumption can almost double in bad cases. Hard water can also result in the formation of horrible greyish-coloured soap residues. These stick to cloth fibers, glassware, ceramic surfaces and food dishes and other products.
| Degree of water hardness | mg/l as CaCO3 |
| Very soft water | 0-20 |
| Soft water | 20-50 |
| Hard water | 50-500 |
| Very hard water | >500 |
You can read a wide range of water usage articles. They discuss the use of water in the house and home ... topics covered include filters, heaters, softeners and water in the garden too. The links change each time you visit the page