The quality of pond water is vital to ensure healthy fish and plant life. Poor water conditions cause fish to lose their colour, behave unnaturally and become prone to disease. Plants will also discolour and show signs of stunted growth. Pond water should always be tested before fish are introduced and regularly monitored throughout the year. Any changes in water conditions can be quickly identified and remedied. pH is a way of expressing whether water is acid, alkaline or neutral. It is measured on a scale from 0 – 14 with pH 7 being the neutral point. Any level below pH 7 is acid and any level about pH 7 is alkaline. Pond fish prefer a pH range of 7.0 to 8.0 although they will survive in slightly acid conditions. Below pH 6.5, fish will show signs of irritation and discolouration. At extreme pH levels, fish and plants will not survive. Pond treatments and beneficial bacteria perform better with a neutral pH. The decomposition of fish waste, uneaten food and decomposing plant material by beneficial bacteria is a process referred to as the Nitrogen cycle.
The first stage of the breakdown results in the formation of toxic ammonia and ammonium. Both are easily converted into each other depending upon the pH i.e. above pH 8.5 – ammonia (toxic): below pH 7.5 – ammonium (non-toxic).
The second state of the breakdown results in the formulation of nitrite. It can be more toxic than ammonia. Nitrite level should not exceed 0.25 mg/l. Nitrite poisoning symptoms are listlessness, oxygen starvation and discolouration. The third stage of the breakdown results in the formation of nitrate. Nitrate is less harmful to fish than ammonia and nitrite. It’s lowest limit of lethal toxicity is 50 – 200 mg/liter. High concentrations of nitrate, in excess of 50 mg/liter, can be harmful to fish and cause unsightly algae growth. Pond test kits are important and easy to use.