The final cocktail
The final cocktail we call water is complex and, as we have seen,
varies with atmospheric and local land conditions. In general, water
from our tap will contain:
major ions such as sodium,
potassium, magnesium, calcium, sulphates, chlorides and hydrogen
carbonate. These are usually present in quantities of at least 1 mg/l.
All of these ions play a major role in the water chemistry of the fish
pond and in many biological functions. They help determine both pH and
water hardness, which are important to fish.
Key nutrient ions, such as
phosphates and nitrate. The concentrations of these are generally
lower than those of the major ions and play a major role in algae
dissolved gases, which
include oxygen and carbon dioxide.
trace ions, such as copper,
iron zinc, fluoride, cobalt and molybdenum, which are important in
minute amounts, but can be toxic to fish at higher levels
As fish-keepers we do not need to know the full composition of the
water that we use for our ponds. The important message is that tap water
is not a simple substance. What we call water is really a weak solution
of several dozen dissolved substances, some beneficial to fish, some
not. (This remark applies to humans, too. Water Boards everywhere devote
a lot of effort to ensuring that water is fit for human consumption.)
When we talk about water chemistry or water quality, what we are really
talking about is the variety and quantities of these various substances,
the reactions between them and their combined effect on the health and
well being of our fish.
So water is variable and has a major influence on aquatic
inhabitants. It is worth recalling that this is of importance to we
fish-keepers because fish are "open" systems, and are strongly
affected by the composition of the water in which they live. We have
seen that tap water is complex, and is further complicated by changes
taking place in the pond. Whether the water coming out of the tap is of
poor or good quality depends largely on your geographical location but
it is fair to say that most poor water quality
in fish ponds arises from what happens in the fish pond, and is not due
to poor supply quality.