There are several water quality parameters that pond keepers need to be aware of.
Ammonia, a waste product given off by life within the pond is broken down by oxygen loving (aerobic) bacteria into Nitrite (less hazardous than ammonia) and then again into Nitrate (much less harmful but a plant fertilizer). These bacteria are growing on every available surface within the pond that has a good oxygen supply. This whole process is known as the nitrogen cycle and as long as there are plants in the pond to utilise the nitrate, the process is complete. An oxygenated pond that is not over loaded with fish can usually provide enough surface area and bacterial growth to look after itself but as the biomass increases (fish growth, addition and reproduction), more bacteria than can live in the pond are required and this is where a biological filter helps by providing a huge amount of extra surface area for the bacteria to grow.
Water Hardness and pH
A pond’s water will naturally acidify (low pH) and soften due to biological processes and this must be avoided. It is better if your pond is topped up by tap rather than a water butt unless the pond has been built with limestone type rocks that will release minerals. This is one parameter of water quality that is usually overlooked but a very important one. The KH Carbonate hardness and GH General hardness should be tested and commercial hardeners, oyster shells or limestone added to the system somehow if either are low.
How long should I run my pump for?
As water warms up, biological processes increase which demand more oxygen. However as water becomes warmer, its ability to hold oxygen decreases. This can lead to the fishs’ oxygen demand being greater than that available especially in hot weather and at night. For this reason, a water or air pump is usually an essential requirement for a pond with fish. Some people only turn their pump on for 2 or 3 hours a day, usually during the afternoon. However, if you are only going to limit the time the pump is on, the 3 hours you should turn the pump on for are the last 3 of the night when plants are actually using oxygen rather than releasing it.
Wonderful bacteria!
Bacteria are doing everything in your pond. Aerobic bacteria are breaking down organic waste in the pond therefore reducing the silt build up, they also break down fish waste into plant fertilizing nitrates and when there are excessive nitrates, anaerobic bacteria will break it down into nitrogen and oxygen which reduces plant and therefore algae growth. The different families of bacteria should be added to ponds during the spring at least to give the pond a kick start after the winter. Depending on conditions and requirements, they can be re-added at regular intervals.