Blanketweed treatment buying guide

Updated: 22 October 2026

amazon.co.uk is offering a mineral powder, a weekly course, a copper liquid, and a preventative as if they were one tub. This blanketweed treatment buying guide only helps once you know which job you are buying. Pea-soup green water, duckweed, and a mat you can lift on a stick are different problems. A treats-10,000-litres line tipped into a 100 litre barrel is an overdose. Prices for the twelve saved listings are on the blanketweed treatment comparison. Peter F. checked those pages on 21 October 2026. This is not a laboratory test. A qualifying purchase can earn a commission at no extra cost to you.

Our top picks

Badge	Product	Job	Stated volume	Repeat	Note	Price	Offer
Best overall	Cloverleaf Cloverleaf Pre-Vent 800 g	Follow-up	Not stated	Every 10–14 days	5.0	about £21.79	View offer
	Cloverleaf Cloverleaf Blanket Answer 800 g	Clear-out	10,000 litres	One dose or monthly	8.6	about £19.47	View offer
	Evolution Aqua Evolution Aqua Stop Blanketweed 4 kg	Weekly course	Not stated	Weekly, then monthly	6.0	about £39.99	View offer

Best overall

Cloverleaf Cloverleaf Pre-Vent 800 g

5.0/10about £21.79

View offer

Rank 2

Cloverleaf Cloverleaf Blanket Answer 800 g

8.6/10about £19.47

View offer

Rank 3

Evolution Aqua Evolution Aqua Stop Blanketweed 4 kg

6.0/10about £39.99

View offer

On this page

1.Hair-like weed, not green water
2.Litres before tub size
3.Four different jobs
4.Price only after the course is counted
5.Which page to open next

Hair-like weed, not green water

The Royal Horticultural Society describes blanketweed as filamentous algae you can lift, sometimes called silkweed, and green water as algae so fine the pond looks like pea soup. Duckweed is a carpet of tiny plants. One Evolution Aqua bullet adds a duckweed claim to a blanketweed powder, which does not make those jobs identical. A June pond in Britain often shows a little of both. Twirl out the strands you can reach and leave that pile on the bank for 48 hours so animals can crawl back. Shade a third to a half of the surface if the pond sits in full sun. A star line is not a diagnosis. Shop products may miss the form of alga you have.

Litres before tub size

Litres are length times width times average depth in metres, times 1,000. A pond 2 m by 1.5 m at 0.5 m average depth holds 1,500 litres. That Pond Guy says measure the volume and do not raise the dose because the water feels cold. Ignore a spec cell that clashes with the title. envii’s bullets say 10,000 litres and a field says 20,000. Use the bullets and 50 ml per 1,000 litres. Stop Blanketweed prints 1 millilitre beside 4 kg and states no litres. NT Labs’ title says 10,000 litres for 800 g while another field says 2 kilograms. Follow the cell that matches the pack weight.

Testsieger

Cloverleaf Cloverleaf Pre-Vent 800 g

5.0/10about £21.79

View offer

Four different jobs

Cloverleaf Blanket Answer is the clear-out. The maker uses 10 g per 125 litres, so 800 g is sold for up to 10,000 litres, with milky water for about five days and the UV left on. The 4 kg tub states 50,000 litres. Stop Blanketweed is a course: 30 g per 900 litres once a week for about three weeks, then monthly, and weaker below 8°C. HSE No. 9647 is Evolution Aqua’s own statement, so check the label. The envii bottle is a liquid for submerged strands and lists copper sulfate. One saved review reports newt deaths. That is one account, not a rate. Pre-Vent is the follow-up every 10 to 14 days, best above 10°C. The bundles do not say how the grams are split.

Price only after the course is counted

These are the saved amazon.co.uk prices. NT Labs is £13.39, the two 800 g Blanket Answer listings are £19.47 and £19.49, envii is £20.95, Pre-Vent is £21.79, Stop Blanketweed is £39.99, and Cloverleaf 4 kg is £64.99. A price per 1,000 litres only works for one treatment with a stated volume. The 800 g tub is about £1.95 per 1,000 litres of a stated 10,000. The 4 kg tub is about £1.30 per 1,000 litres of a stated 50,000. NT Labs is not the value pick, because the review file is not a pond sample. Stop Blanketweed has no listing litre figure, and the maker’s weekly programme spends the tub across repeats. If the tub is chosen, the order of work is on the how to use blanketweed treatment page.

Which page to open next

If the pond has frogs or newts, read the wildlife page before a copper liquid. Named picks sit on the best page. Straw as a suppressant sits on the barley straw page. This guide is the if-then: hair you can lift, a litre sum that includes the shelves, then the job the label describes.

Common questions

Is this blanketweed or green water?

Blanketweed is the hair you can lift on a stick. Green water is a pea-soup cloud, and the Royal Horticultural Society treats them as different problems. If you cannot lift strands, you are in the wrong aisle even when the listing mentions algae in general. A pond can show a little of both after a warm week. Size the treatment to the mat.

Is an 800 g tub enough, or do I need 4 kg?

The 800 g Blanket Answer listings state up to 10,000 litres. The 500 g tub states 6,250 litres. The 4 kg tub states 50,000 litres. Under 10,000 litres, the 4 kg tub is leftover powder. Near 50,000 litres, 800 g does not cover the pond at 10 g per 125 litres. The 25 kg tub states 312,500 litres and has no star line.

Is Pre-Vent the same job as Blanket Answer?

Blanket Answer is the clear-out powder. Pre-Vent is the follow-up every 10 to 14 days, best above 10°C, and the listing states no treat volume. A 4.9 from 27 reviews does not clear a solid mat. The bundles name both products and do not say how the grams are split.

Why is Stop Blanketweed not a one-dose bargain?

The maker’s programme is 30 g per 900 litres once a week for about three weeks, then monthly, and it is weaker below 8°C. The saved 4 kg listing at £39.99 states no litres. HSE No. 9647 is the maker’s own statement. Check the label before you treat that shelf price as one Saturday.

Can I trust the NT Labs star line?

The saved page is 4.1 from 15 ratings, and several of those reviews are about brine shrimp rather than a pond. The title states 10,000 litres at £13.39, and the bullets tell you to aerate when oxygen is likely to be low. That instruction is usable. The star average is not fifteen cleared ponds.

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