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Viresco (UK) Ltd Tel: 44 (0)1845 525585 Fax: 44 (0)1845 523133

Viresco (UK) Limited is a company registered in England and Wales with company number 5079726 VAT No: 481 9223 35 © 2003-2012

Suppliers of speciality products for the amateur pondkeeper and gardener worldwide

Blanketweed Control Trials

“Gardening Which” – May 2007

During 2006, “Gardening Which” conducted a major trial on 21 different algae control products.  Our Viresco™ Aqua was one of the 21 products.  In the May 2007 issue, 6 products were chosen as the “Best Buys” and one of these 6 was Viresco Aqua.  The products were marked out of 5 for certain aspects  - greenwater control, blanketweed control and ease of use.   Four of the products were given 9 points out of 10 for blanketweed and greenwater control with the other 2 being given lower marks.  Three of the 4 products, including Viresco™ Aqua, were given 5 stars for blanketweed suppression and 4 stars for greenwater (algae bloom suppression). 

The costs of application were also given.  One of the other six “Best Buys” was shown as the cheapest to use – 49p per 1000 litres.  Another was costed at 89p.  Our Viresco™ Aqua was the next best value at 97p.  The costs of using the other 3 products ranged from £1.60 to £2.58.

These costs are for one application only.  However, the pondkeeper wants to know how much the treatment costs for a full season when he uses the number of doses recommended by the manufacturer.  This was not calculated in the “Gardening Which” feature.  This is a repeat of what was done for the “Koi Ponds and Gardens” Summer 2004 publication.

When the full annual treatment costs were calculated, these were as follows:    

Annual Cost of Using Algae Control Products

“Best Buy”

Cost of
First Dose

Subsequent Applications

Number of

Cost of Subsequent

Total Annual Cost

Times the Cost of Viresco™ Aqua







  5.05 x



Every 4 Months




10.64 x



Every 4 Months




  6.60 x



14p per week




  7.85 x



Every 2 weeks




41.24 x

Viresco™ Aqua







Thus, of the six “Best Buy” products, Viresco™ Aqua is the best value for money by far when the full annual costs are taken into account.

»  Click here to view the full article

"Koi Ponds & Gardens", September 2000

David Brown who used to do research and writes for "Koi Ponds & Gardens" in the Summer of 2000 carried out some trials using Viresco™ Koi in his 4000 gallon pond.

He introduced the product into his pond on June 26th. The initial reading of nitrate was 80ppm and that of phosphate was 10ppm. Blanketweed was growing at approximately 2 feet (60cm) per day.

David took daily readings of the nitrate and phosphate levels in the pond after applying Viresco™ Koi and after 9 days the nitrate had dropped to zero and the phosphate level had been reduced to 5ppm. The graph below shows how the nitrate and phosphate levels reduced over time.

Once the nitrate had dropped to zero, the blanketweed, which had been slowing down in growth, died. The nitrate remained at zero for about another three months after which time David emptied his pond to rebuild it. Blanketweed remained absent for this three month period.

Regarding the phosphate levels, it can be seen from the graph that after 6 days, the phosphate reading rose. David concluded that this was caused by the introduction of some montmorillonite clay at that time. He tested it to find it contained a significant amount of phosphate.

»  Click here to read the details on this trial

"Koi Ponds & Gardens", August 2001

During 2001, Brooksby College in Leicestershire were asked to undertake some blanketweed trials by "Koi Ponds & Gardens" magazine. The results were published in the August issue of the magazine under the feature entitled "Beat the weed". Six blanketweed control products were tested. Two were electromagnetic, one was a water purifier with a copper releasing cartridge, one was a water colorant and two were microbial. The product brands that were compared were:

»  Pondweeder
»  Water King
»  Aquastar
»  Nishicare
»  Kusuri Eco-Pure and
»  Viresco™ Koi
Blanketweed Trial for
"Koi Ponds & Gardens"
Viresco™ Koi
star ratingstar ratingstar ratingstar rating
Kusuri Eco-Pure
star ratingstar ratingstar rating
star ratingstar ratingstar rating
Water King
star ratingstar ratingstar rating
star ratingstar ratingstar rating
star ratingstar rating

Fourteen vats containing blanketweed were set up and each product was tested in two vats. The final two vats were used as control. After two weeks following treatment, the weight of the blanketweed in each vat was checked and an assessment made of the results.

Our Viresco™ Koi was declared to be "The Winner" and given 4-star rating. Four of the products were given 3-stars and the sixth, 2-stars.

»  Click here to view the full article in "Koi Ponds & Gardens"