Pond algae treatments. What does the label on the bottle mean?

Green water and pond algae problems such as blanketweed and string algae are annoying. The most common problem that ponds experience surprisingly does not relate the to fish, but to plants, – and unwanted ones at that, such as green water and blanketweed.

Algae problems in koi ponds have risen to become one of the koi keeper’s most common complaints.

Algicides. Interpreting the label

Nuisance algae will usually take one of two forms; green water and filamentous algae known as blanketweed. Ponds are rarely algae-free as these two forms of algae appear to work in partnership to curse koi ponds. For example, if a pond has benefited from a UVc, clearing it of green water,

then blanketweed will proliferate, thriving in the clear sunlit pond water enriched with nutrients.

If however, a pond suffers from green water, then there is little chance of blanketweed troubling the same pond.

And then there are those few unfortunate ponds that appear to suffer from both forms of nuisance algae at the same time.

The majority of koi ponds will fall into the first category, where crystal clear water, courtesy of a UVc is prone to being choked with unsightly fronds of hair-like blanketweed. Having cracked the green water problem with a UVc, the koi keeper’s final assault on blanketweed may well involve a variety of treatments that are added to the water to solve the problem.

Blanc-Kit Excel is specially formulated to create a pond environment resistant to blanket weed without the use of harsh chemicals

When comparing the different chemical blanketweed treatments, it can be useful to be able to interpret the label to see if a particular product will do what you want it to.

Checklist of what to look out for on a label of a chemical treatment for blanketweed.

Description of the product

Volume of pond water treated

Course of treatment

Warnings or precautions


Description of the product

Scanning across labels of different products for blanketweed, various claims are used such as ‘controls’, ‘clears’, ‘deals with’, ‘reduces’ and ‘kills’. A product that controls does just that, it reduces and inhibits growth. That may be different from a treatment that ‘prevents’ blanketweed from growing.

Such a product does not claim to eradicate it completely, in fact there appears only to be one product that kills blanketweed and that is the product ‘Blanc-kit’.

This pond treatment contains a herbicide that will definitely kill blanketweed.

How do the other products work?

Blanketweed treatments that ‘control’ or ‘deal with’ blanketweed growth may use a combination of dyes that turn the water blue, thus shading algae from its valuable sunlight thereby reducing its growth. The longer the dye is in the water, the longer the blanketweed is starved of light. Other blanketweed and algae controls use additives that lock up the nutrients that algae require to grow. Again, these products do not kill blanketweed, they control, reduce or deal with its growth.

Volume Treated.

The label of a treatment will specify the volume of pond water that it will treat (in litres and gallons) and this can be used to determine how many treatments you may get out of each pack.

Course of treatment.

Some products state ‘regular’ use while others are more specific with ‘monthly’ doses or applications ‘every 4 months’ recommended. This should determine the size of bottle or pack required, as some products require regular dosing while others may last for 4 months

Warnings or precautions

Warnings or precautions on packs are for the benefit of you and your koi. Some products state ‘has no detrimental effect on fish and plant life’ others state ‘harmless to all fish’, but may turn your water blue.

The only aquatic herbicide on the market (Blanc-kit) is ‘safe to use in ponds containing fish, emerged plants such as reeds and rushes’ but may suppress or damage certain desirable plants such as water lilies.

Blanc-Kit Excel is specially formulated to create a pond environment resistant to blanket weed without the use of harsh chemicals

However, if your koi pond is completely plant-free, then it can be used without any worries.


Price is an important consideration when comparing the products’ claims and the volumes of water they will treat. Is an algae killer that treats 1500 gallons better value than a similarly priced blanketweed controller that treats 3000 gallons? The decision is yours.

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