Whether your keep a rainwater tank for potable water, irrigation purposes, or just something to water the flowerbeds with, algal blooms lurking within your collected rainwater supplies can be a difficult problem to deal with. Algae can badly affect the taste of drinking water, and can cause nasty gastrointestinal upsets in large concentrations, while watering plants or lawns with water contaminated with algae can alter your soil chemistry and cause hoses, irrigations pipes and sprinkler heads to clog. Luckily, it's a relativity easy process to prevent algal blooms from appearing in your rainwater tanks, and if algae still manages to slip through your security, there are ways to remove it.
Preventing algal blooms
A number of different algae species can appear in your rainwater tank, but they all share one thing in common -- without light, they cannot live. Keeping sunlight out of your rainwater tank whenever possible is always the most effective way to keep algal blooms at bay, and there are a number of ways you can go about it:
- Rainwater tanks should be as opaque as possible, as even a slightly translucent white tank can let enough UV light through to stimulate small-scale algal growth. If you have a plastic tank, make sure it's thick and dark enough for no light to penetrate. Even something as simple as painting the outside of the tank black can keep light out effectively.
- Be sure the lid is fastened tightly and securely at all times, and be sure to replace a lid properly after removing it to draw water or inspect water quality. This can be a problem with older, concrete rainwater tanks, as they do not provide a tight seal between the main body of the tank and the lid. Choose a plastic or metal lid with an airtight seal, and make sure to inspect it regularly to check for cracks or rust which may allow light through.
- Gutters and inlets should be long enough to ensure that light never shines directly down them. They should also be fitted with tight gauze filters, both to mask UV light and to filter out other harmful contaminants.
- The first rain of a season should always be discarded, as it contains dormant algal spores and other contaminants that accumulate on your roofs and gutters during dry months. Many rainwater tanks now come with first-flush devices to automatically discard early rainwater, and these should be maintained well.
How to remove algal blooms
If, despite all your best efforts, you still spot the tell-tale mats of algae floating on the surface of your water, there are a couple of options available to you:
- Algaecide is effective and relatively inexpensive. However, it's important to choose the right algaecide for your needs, as many are intended for use in swimming pools and will render water unfit for human consumption. Some may also contain disinfectant solutions that can adversely effect plants. Choose a safe algaecide rated for human consumption wherever possible, and be aware that particularly large algae mats may require several rounds of algaecide to be completely eliminated.
- Draining and cleaning the tank is the other option, and it is often the only option for chronic algae problems. Before you do this and waste your accumulated water, you should make sure that the tank itself is not the problem, as a cracked or leaking water tank will allow algal growth even after cleaning and must be repaired or replaced.