How To Use Viresco Koi & Viresco Aqua In Garden Ponds? Viresco is the only product I have been able to recommend in the many years of selling pond products. Not only does it work fantastically well but it is a natural product, has long life and low cost per unit of pond volume unlike expensive blanketweed chemicals whose effectiveness is suspect and can create other pond problems associated with using powerful chemicals (essentially weedkillers)… This is especially true where pond plants are concerned.

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Introduction to Viresco for Algae and Blanketweed Control in All Fish Ponds

Viresco AQUA and Viresco KOI are based upon 2 different micro-organism mixtures. The same highly concentrated freeze dried product is packed into different (but small) packs to cater for ponds up to almost 70,000 litres. Viresco AQUA and Viresco KOI are essentially a mix of organic destroying bacteria and bacteria that remove nitrates. These latter bacteria turn the nitrate into gaseous nitrogen which escapes into the environment. Because all the available nitrate food for the algae is consumed by the Viresco AQUA and Viresco KOI then the algae…

The algae whether it be blanket weed or suspended algae literally starve to death.

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Testimonials and feedback from past clients are great! See some of our happy Viresco clients below:

HI, im fairly new to your site but have already downloaded your book and taken some of your advice, would just like to say a massive thank you as your info has helped me to finally solve my pond problems and thanks to your advice to use Viresco to solve blanket weed etc i now have a clean, crystal clear pond and no blanket weed or algae in sight!! my fish are also reeping the benefits of this fab product, Cant beleive it works as in the past have spent a fortune on other so called removers to no avail so its fantastic to find a product that actually works.
I live in the uk and weather here is unpredictable but least now i can enjoy my pond all year round thanks to yourself and the great discoverer of Viresco so congratulations on a great site and many thanks for your helpfull and intuative book and emails.

Kindest Regards


After reading your article on email I purchased a packet of Viresco for my pond.The pond water is now clearing, brilliant to see my fish again. Thankyou very much. Also would you know why my goldfish in a small indoor aqarium tank have turned black in colour.they look as if they have a black film over them,one of them has now returned to gold again,the fish are eating and swimming well,any ideas ?
Hi Anthony,

I am a fairly new koi pond owner (less than a year) and I must say I am still learning everyday. I had a very trying time with blanket weed, and it really got me till I tried Viresco. Initially I expected results with in at least three weeks after introducing it into my pond (5000Lt) This system has taken a good 6-8 weeks to kick in with optimum performance reached after ten weeks. One thing you don’t mention in your comments is patience.It is very frustrating and you want to give up, when you see other people’s clear water and blanket algae free sides, but everything takes time, and one must not get into the sense of false security by jumping from one remedy to the next to try and get rid of the blanket weed. New comers should also be taught to leave the pond alone so that it can sort itself out, with the correct biofilter and Viresco it will come right.
I am amazed, because I have a closed system, without a drain I stir the pond up once a month and then filter use extra external filters, sponges to trap the residue waste The amount that comes out is minimal and the water and sides are crystal clear within an hour.
My fish have doubled in size and are very healthy. I truly believe the answer lay in the use of Viresco, initially I was skeptical, and disappointed but with time and patience it has worked out.
I most certainly be getting a fresh supply before the summer starts. New pond owners must not be put off by the cost, it is worth it in the end.



The Viresco products (AQUA, KOI and DIGESTER) are all powdered and are all dry. They have unlimited shelf life. The micro-organisms are freeze dried and are carried on fine particles of bran. The rest of the product consists of nutrient materials which, when added to water, dissolve to provide a food source for the bacteria microbes as they come back to life.

How Viresco works

How Much Viresco To Apply and How Frequently

Viresco CycleOnly small initial concentrations of the bacterial mix are required. This initial addition grows rapidly on the pond water nutrients and additives in the initial freeze dried mix. In most ponds it is sufficient to add a single addition that will last for a considerable period of time. However take this with some caution since every single pond is different and you may find in some circumstances that an extra occasional maintenance addition would be beneficial. What’s important to bear in mind is that there is no need for weekly maintenance additions as is the case with chemicals.

The microbes supplied will last (in theory) as long as the available food supply (nitrates) is present in the pond and fish produce nitrogen chemicals as a normal metabolic process. In practice an occasional top-up is recommended

Nitrate in the pond water will be reduced down to zero when either Viresco Aqua or Viresco Koi is used and when this happens, algae, in whatever form, will die from starvation. Phosphate will also be reduced but from tests carried out, the phosphate level drops more slowly and never drops to zero. However, whilst algae needs both phosphate and nitrate to grow, just getting the nitrate down to zero is enough to cause death of all algae materials including blanket weed

Please note Viresco is not a chemical and takes some weeks before becoming fully effective. It takes time for the bacteria to reach the levels required to consume nitrates at a rate which they are produced. Avoid pumping out water and replacing with fresh water unless absolutely necessary.

Where To Use The Different Products

Viresco Koi contains mainly nutrient remover bacteria and little waste digesting bacteria and microbial life. Use it therefore to control blanketweed and algae in clean koi ponds. These ponds normally have bottom drains and the pond keeper uses vacuums and skimmers. Therefore little organic debris should be present in the pond.

Viresco Aqua should be used to control blanketweed and green water in all other types of fish ponds. Most fish or garden ponds do not have bottom drains or skimmers and use of a vacuum is not normal. Ponds with aquatic plants of all kinds should be treated with Viresco Aqua.

Viresco Digester is for use when the organic waste in a pond is high and if you need to handle a specific problems such as excessive build up of organic matter in under gravel filters. This type of microbe mix is ideal for those situations where sand filters are used (such as here in South Africa). The digester bacteria will remove the build up of fats and protein on the surface of the sand particles.

Viresco Aqua and Viresco Koi are available in 5g, 10g, and 25g packs. These will treat pond volumes shown below:

Viresco Aqua and Viresco Koi pack size and treated pond volume

Pack Size/Type
Pond Volume Treated

Viresco Aqua 5gms
5 gm treats 13,600 litres

Viresco Aqua 10gms
10 gm treats 27,300 litres

Viresco Aqua 25gms
25 gm treats 68,200 litres

Viresco Koi 5gms
5 gm treats 13,600 litres

Viresco Koi 10gms
10 gm treats 27,300 litres

Viresco Koi 25gms
25 gm treats 68,200 litres

Viresco Koi suggested for ponds with bottom drains. Viresco koi suggested for all other ponds
Usually one application is enough to reduce the nitrate level to zero and keep it there for a number of weeks or months. Customers make one application and then are free from blanketweed for more than one year in many cases.

Viresco PacksSome other customers need more than one application of Viresco Aqua or Viresco Koi. The pond keeper is advised to check nitrate levels, say, once or twice per week to see how the Viresco Aqua or Viresco Koi is reducing nitrate (keep a simple graph going). Many people see nitrate moving to zero in less than a week while for others it can take a few weeks to drop to zero. If hardly any change is seen say, within, three weeks, add another dose or part dose.

We would suggest that the pond keeper considers the application of maintenance doses. We don’t recommend specific amounts at specific times. Our microbial mixtures do lose some of their viability over time as each generation of new ones succeeds the previous. So we do suggest regular nitrate testing as an indicator of when more product might need to be applied.

However, every pond is different and each pond keeper will do things differently. One customer decided to double dose with Viresco Koi to begin with and then to put in half a dose every two weeks. This turns out to be a successful method for him.

How To Apply Viresco Aqua and Viresco Koi

Dissolve the freeze dried powder in a small amount of pond water, leave for a few hours and then bulk up with more pond water before adding direct to the water in different places around the pond. Ideally the powder should be mixed in the morning, left with an air-stone and added into the pond in the evening. Intermittent use of a cake or egg whisk can be made if an air-stone is not available.

It is important to keep the mixture in a shaded place indoors once you dissolve in water. This is because the UV radiation from daylight could damage some of the bacteria in our products.




DO NOT USE TAP WATER which contains chlorine

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