Algae Facts & Treatment Information

Algae, what’s it all about?

Algae is not harmful, so don’t panic, it is a natural food source, a fish breeding ground, and a shelter for baby fish and tadpoles to start their new lives. In fact fish are generally happier in green water, but visually it is unattractive to us as we want to see the clear water.

Algae is a primitive plant that is exclusively aquatic, ranging in size from microscopic to large filamentous strands, with colour varying from black/brown through to bright green. Its texture can range from slimy to quite a dry hairy feeling.

Algae will grow in nearly any body of water, you can place a bucket of fresh water in a sunny spot and over time algae will grow.

Filamentous algae is seasonal and will general grow more rapidly in spring and at the end of summer.

Single celled or green water algae can be present at any time, this generally occurs in new ponds during the first 4-6 weeks, when filters are cleaned out too often and ponds with no or incorrect filtration.

What is considered normal in a pond?

A balanced normal pond will have a fine layer of soft algae growing on the sides, up to 2-5cm in length; there will be fluctuations of water clarity over the year and fluctuations of the amount of filamentous algae growing.

What to do about green water?

Green water is easily managed.

Firstly by filtering, this means pumping the water out of your pond and into some sort of filtration device, be it a plant filter or a biological filter, returning clear and clean water back into your pond. Filters are easy to set up and maintain and will greatly assist with the health and clarity of the water – with correct filtering you can expect water to clear within 1-4 weeks. You need to run your pump and filter system 24 hours a day and you need to have the right sized pump and filter for your pond (speak to us we can tell you what you need).

UV light units will sterilise water, killing and causing the singled celled algae to clump together to form larger particles, which in turn will be trapped in the filter. UV units can be expensive and the globes need to be replaced annually, but they do offer a year-round clear water guarantee. Most biological pressure filters include UV lights/.

Bacterias such as Splosht and Pond Enzyme can be added regularly to the pond to help clear green water – expect a 4-8 week process as the bacteria is a natural product that will grow and populate within the pond.

If you don’t want to use a pump or filter, then you will need a 10cm layer of fine gravel on the base of the pond, add lots of aquatic plants (go for about a 75% coverage), add bacteria, add Zeolite gravel (naturally occurring volcanic rock). It could take up to 6-12 months to mature and achieve complete clarity, but it will happen.

What to do about filamentous algae (string algae/blanket weed)?

This is such a common concern, but don’t despair! It may look unattractive but it is not at all harmful to the ecology of you pond. In fact it can be very healthy and helpful by providing a great place for fish and frogs to spawn, a place for baby fish to hide, and a great natural food source for both fish and frogs. Think of it as weeds in the garden and pull it out by hand if it gets too much to look at.

A healthy chemical free pond will always have some algae. You can manage its growth by having high fish stocks and good filtration, and removing by it by hand.

You can regularly use Zeolite sand/powder (naturally occurring volcanic rock) – swish enough through the water to create a cloud across the pond, coating any algae growing. You will need to do this every 1-2 days, pulling out by hand anything that you can as you go. This generally takes about 2-3 weeks to get under control. Use small amounts of Zeolite anytime you think you need to, and yes it is fully safe for fish, frogs and plants.

If you have large pebbles (anything over 6cm is considered large) remove them from the pond. Large pebbles or stones assist algae growth by giving the algae extra surface area to cling to. Smaller 3-5mm gravel will be small enough for the fish to move around, effectively cleaning it for you. Having a 10cm thick layer of the gravel covering the base of the pond allows beneficial bacteria to grow within it, and help consume fish waste that falls to the bottom.

Chemicals?

You will note that we have not mentioned any chemicals as a way to control any of the forms of algae. Dosing with chemicals and algaecides (including those that say they are fish and plant friendly) without remedying any underlying causes, will only ever give temporary respite at best. Algae is just a plant and any chemical that can kill algae can have an effect on the other plant life and fish in your pond, as chemicals cannot distinguish between what you want to kill and what you want to grow.

Ponds are living things harbouring a large range of life, they are not swimming pools or spas. If you take a natural, realistic approach to water gardening then you can expect clean, clear water, expect healthy fish and plants and expect algae at different times or the year.