Cures for green water, algae and blanket weed (spirogyra) problems.

Potentially a beautiful and serene pond in late spring marred by sight of blanket weed. The stone is limestone so the water has a high pH making the weed a difficult problem to eradicate.

All water exposed to the environment for any length of time contains algae. Algae are not a problem themselves under normal conditions. In fact some species can be a sign of healthy water and they make a vitamin rich snack for fish. There are others that are specific to different conditions of water and various forms of pollution. Some make the water smell or taste peculiar and others in large quantities can make the life very uncomfortable for fish. Their proliferation may be a symptom of any of the above effects and therefore the cause or causes are the problem or as in some cases it may be caused by the natural environmental swings, like simply the weather and time of year. In order to restrict the growth of algae and minimise the effect and to restrict their prolonged proliferation:

1. Increase the oxygen level of the pond. Aerate either mechanically by moving the water through stream or fountain or by plants. Increase the numbers of oxygenating plants. These will compete with the algae for the same nutritional minerals in the environment. They will also provide oxygen for the bacteria in the bottom of the pool or filter and thus provide a welcome boost to the life/nitrogen cycle of the pond.

2. Floating plants are a quick and effective addition to the pool because they provide shade and use up the plant nutrients in the pool that might otherwise be capitalised on by the algae. Water Hyacinth (Eichornia crassipes) works particularly well, although it is not welcome in the warmer parts of the United States and in South Africa because of its tendency to clog up waterways and dams.

3. For the longer term - Lilies provide shade and use up any nitrates that may be in the water. In fact all other plants are on your side. The marginal plants are helping to use up the nitrates that even the most efficient biological filter cannot deal with.

4. Remove excess fish. Avoid having more than 2inches of fish per square foot of surface area, that works out as half a metre of fish for every square metre.

5. Only feed them what they can eat in 5minutes. Floating fish food is suitable for most fish as any excess can be netted off.

6. If you have any shallows and backwaters then these can become 'algae factories'. Try to get some higher plants established in these regions. What is the point in having a beach effect if it always covered in blanket weed.

7. If you haven't already got a biological filter then consider it. You may only be buying time if there is something else inherently wrong with your pool balance. Also remember that if the problem is caused by persistent pollution this will not be a 'cure' as such.

Once you have a filter you are committed to running it all day and everyday apart from in the very frozen depths of winter.

If you have got a filter - Is it big enough and is the pump that is feeding the filter water, turning over the total volume of the pond every 2 hours?

Is the pump well away from the filter unit so that all the water in the pond gets circulated through the filter?

8. If you haven't already got a U/V sterilizer, then consider it. But you will need some sort of filtration system as well. It is essential that it treats the water going INTO the filter.

Keep the quartz sleeve clean. A further device in the form of a magnet that lies in line before the U/V supposedly helps prevent hard water from building up deposits on the inside of the unit. It also discourages the build up of the long strings of cell growth in blanket weed.

9. If you have a large Koi 'setup' that does not have the benefit of plants to do the work in the final stage of the Nitrogen cycle that is using up the nitrates in the environment then you can consider an anaerobic stage to your filtration. Here an extension to the filter using aerobic bacteria digesting basic organic material, passes water much more slowly through a medium in which a colony of anaerobic bacteria is established. These bacteria work much more slowly and do not need oxygen to survive. They are capable of breaking down the nitrates into their basic oxygen and nitrogen building blocks. Alternatively, see the REED BED SYSTEMS.

10. If you dont want to become dependent on technology, try Barley straw. It works for most people. But you need plenty of oxygen too.

Recipe: 5grams of Barley Straw per 1000 litres (220galls) of water.

• Pack into open meshed sacks

• Keep straw on the surface and exposed to sunlight

• Circulate water to distribute effect.

• Ensure the water is well oxygenated.

• Allow 1 full month for it to take effect.

• Replenish every 6mths.

The retailers and manufacturers of Barley Straw 'products' assure me that although Barley Straw will not eradicate huge massed quantities of blanket weed, if the customer does his or her best to remove the majority of that which plagues him then the chemistry will begin to work in his or her favour.

11. For 'natural style' pools, products like 'Aquaplankton', which come as a powder that stimulates the bacterial growth in the bottom of the pond, are worth trying. The pond needs to be well oxygenated for the products to work effectively.

12. If you have not got fish, introduce Daphnia. These tiny creatures (which fish love to eat) consume algae. If algae flourishes then so do they and so they are the perfect natural control.

13. It is important, as well, to shift down the pH of the water particularly for the control of Blanket weed. Blanket weed only develops at pH above 7.

Also when the pH rises, the toxic effect of any ammonia in the water rises. Therefore stress from any lime in the water is made that more unbearable to the fish by their own ammonia excretions.

The pH of pond can be effectively reduced with chemicals or a 'peat pellet teabag'. The latter method is rapidly losing favour with the avoidance of using the non-renewable resource of peat.

14. Many peoples' opinion is that Green Water is dirty water, but having read this far we now know that is not necessarily the case, but the truth may be that the situation has got well beyond the help of any filtration or chemical inoculation and the pool, quite simply, needs a good clean out!

Remember that if you do go for the complete clean out option you will have to wait for your new pond water to go through an 'aging' process, which generally means it will turn (hopefully temporarily) green. Treating fresh tap water with a water conditioner can sometimes avoid this phase.

Running the water in from a height, and letting it splash in, helps. This dissipates at least half the chlorine in the water, but unfortunately not the more stable chloramines that is also put in nowadays. This may take another three days to disappear.