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even more weeds
By John | February 2, 2008
Algae in pools/ swimming ponds
Algae can cause ‘pea soup’, blanket weed or floating scums. As well as looking unsightly, excessive algal growth, encouraged by surplus nutrients, can lead to de-oxygenation of water with a consequent detrimental effect on aquatic life.
Causes
Excessive algae forms when there are too many nutrients in the water, due to a build-up of organic matter (sludge) on the bottom, fertilizers leaching into the pond or regular topping up with tap-water. Chemical treatments are available but practical solutions are simpler, cheaper and usually longer acting.
Prevention
Ensure a minimum pool depth of 75cm (2.5ft) as shallow pools warm rapidly, sunshine speeding up algal growth. Use black liners to minimise heat reflecting into the water.
Remove any soil from the pool before filling, and only immerse plants in containers of aquatic compost, surfaced with shingle. Apply fertilisers to nearby lawns carefully, as run-off can occur after heavy rain.
Ensure oxygenating plants are present in sufficient quantities. Aim to have at least one third of the pool’s surface area covered with oxygenating or other aquatic plants. Avoid over-stocking with fish, which produce nutrient-rich waste.
Net the pond in autumn to prevent leaves (nutrient source) from falling into the water.
Control
Changing water upsets the natural pool balance. Remove blanket weed with a rake; duckweed can be skimmed off or removed using a net. Remove sunken debris every few years. Clean ponds in early summer, after aquatic life has bred. Divide aquatic plants at this time.
Submerge mesh bags of barley straw (or lavender clippings in larger ponds) just below the water’s surface in early spring, replacing them when they turn black. Chemicals released through straw decomposition inhibit algal growth. Roughly 25-50g of straw per sq m of water surface area is required, depending on the severity of the problem.
Pond filters can be installed, removing algae and nutrients through mechanical and/or biological methods. Consult specialist suppliers regarding you requirements.
Topics: Flora & Fauna |
