When you first fill a pond it should be done using tap water. Rainwater is generally too acidic for fish and for most aquatic plants. Rainwater is only suitable if it has been properly filtered first. Tap water contains varying levels of chlorine, which can irritate the mucous membrane of fish. It is for this reason that ponds should be left to stand for a few days before introducing fish so that the chlorine gases can escape first. The warmer the weather, the quicker the gases will escape and therefore you will only need to wait a few days before adding fish to your pond versus colder weather when the process is slow.
The pH of pond water should be between 6.5 and 7.5. If the pH is too low (acidic) you can add soluble lime to the water. A measurement too high will often indicate “hard” water, or water that has too much calcium and/or magnesium. Peat moss added to your pond water will soften it by binding the calcium and magnesium ions while simultaneously releasing tannic and gallic acids into the water. These acids then attack the bicarbonates in the water, reducing the water’s carbonate hardness and pH. Use a media bag large enough to contain a good amount of peat moss and place the bag in a location where water flow is high. Peat moss will help stabilise pond water, but should be used sparingly as to not interfere with pond plant or animal life.
Good water quality and an ecological balance are also dependent on nutrient levels of the water. Nutrients coming into a pond need to be used up. Nutrients can enter via rainwater runoff, from the breakdown of dead plant and animal tissue and uneaten fish food. Nutrients are needed by plants during spring and summer growing seasons, but if there is more than needed algae growth will appear. Too much algae can rob a pond of oxygen and suffocate life in the pond.
To keep the water in your pond neutral there are things you need to do:
- Any soil added to the pond bed must be poor in nutrients.
- Keep water soft and lime-free
- Plant underwater vegetation
- Feed fish sparingly to avoid uneaten food falling to the bed of the pond and attracting bacterial growth
- Remove filamentous algae and dead vegetation.
If you have to do any maintenance work on your pond or repair a pond liner, it is advisable not to change all of the pond water as fresh water will only bring added nutrients, which will disturb the balance. If you need to do maintenance, leave in at least a third to a half of the water.