How to dose pond clear
Updated: 22 October 2026
You are at the pond with a tape and a bottle, and the water is too green to judge the depth by eye. How to dose pond clear starts with the litres you have, then the rate on that bottle, not a figure copied from another brand. A rectangular pond 3 m long and 2 m wide, with an average depth of 0.6 m, holds about 3,600 litres. Taking the 1.2 m sump as the depth of the whole floor would treat that as 7,200 litres. The steps below are for the six listings on the [pond clear comparison](/hub/garden-ponds/pond-clear). They do not rank those bottles. This is not a laboratory test.
You are at the pond with a tape and a bottle, and the water is too green to judge the depth by eye.
You are at the pond with a tape and a bottle, and the water is too green to judge the depth by eye. How to dose pond clear starts with the litres you have, then the rate on that bottle, not a figure copied from another brand. A rectangular pond 3 m long and 2 m wide, with an average depth of 0.6 m, holds about 3,600 litres. Taking the 1.2 m sump as the depth of the whole floor would treat that as 7,200 litres. The steps below are for the six listings on the pond clear comparison. They do not rank those bottles. This is not a laboratory test.
Our top picks
| Badge | Product | Dose on the listing | Stated treatment | Repeat | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Envii Envii Pond Klear, 500 ml | No ml rate on the listing | Up to 20,000 litres | Weekly on the listing | 7.8 | about £12.95 | View offer |
 Blagdon Blagdon Green Away, 250 ml | No ml rate | 250 ml treats 5,000 litres | Next day only if the first partly worked, on the FAQ | 8.4 | about £7.95 | View offer | |
 Envii Envii Pond Klear Xtra, 1 litre | 10 ml per 1,000 litres | Up to 100,000 litres as a sum | Not a same-day second pour | 7.7 | about £31.95 | View offer |
Litres before millilitres
You get litres from length times width times average depth times 1,000 when the measurements are in metres and the pond is close to a rectangle. The deepest point, including a pump sump, is a hole in the floor, not the depth of the water you are treating.
Take 3 m by 2 m by 0.6 m as a rule of thumb you can check on the ground. If half the floor is a shelf at 0.4 m and the other half is 0.8 m, the average is 0.6 m, and that sum is 3,600 litres. Enter 1.2 m because that is where the pump sits and the same formula returns 7,200 litres, a dose for water that is not there. Measure shelves as separate boxes and add the litres.
A UK gallon is about 4.546 litres and a US gallon is about 3.785 litres, so a calculator that still means American gallons understates a British pond. Convert with the UK gallon if the pack forces you to, then dose in litres.
The rate on these listings
These six listings do not share a millilitre rate. Envii's 10 ml per 1,000 litres belongs on Envii Pond Klear Xtra. Putting it on Tetra CrystalWater or Blagdon Green Away doses a different liquid. Where the amazon.co.uk text is blank, a manufacturer page is a separate source, not a bullet on that listing.
Xtra prints 10 ml per 1,000 litres. On the 3,600 litre example that is 36 ml. The 500 ml Pond Klear listing states weekly use and up to 20,000 litres, and it does not print millilitres. Envii's product page, not the Amazon bullets, states 25 ml per 1,000 litres, every 7 days, and 6 to 8 weeks when the pond is very murky. If the label does not show 25 ml, do not add it.
Blagdon's 250 ml listing says the bottle treats 5,000 litres and prints no millilitre rate. Its FAQ, not the listing, gives pH 6.5 to 8.5 and a second dose the next day only if the first partly worked. Tetra's listing prints no dose. Tetra's UK page states 50 ml per 1,000 litres, and fish-loss reviews are a reason not to treat that page as the listing text. AquaDesign states 2,500 ml for 12,500 litres and a 3 ml pipette, with no rate. NBOFOL prints none. Follow the pack you bought, or the pond clear buying guide, rather than a neighbour's number.
Pour, then wait
Pour the measured amount into a bucket of pond water when the label asks for that, which is how Envii's Pond Klear page describes the mix, rather than into tap water. Keep the pump and the air running unless your own label says otherwise.
Cloudiness the same day can mean particles are clumping, and it can mean the pour was heavy. Tetra's page warns of temporary turbidity. Milkier water this evening is a reason to wait, not to open a second bottle. Pond Klear is weekly on Envii's page, while a clumping bottle is sold as a faster change that can look worse first. Pouring both the same day stacks two mechanisms you have not timed. When the green returns later, the causes sit on the clear green pond water page.
When to stop
Stop if fish gasp, hang under the surface, or roll. One AquaDesign review reports a drop in oxygen. NT Labs' Magiclear label, a different product, warns about oxygen in thick pea soup, so that warning is not a result for your bottle. Aerate, and if the fish do not settle, call a pond specialist rather than adding a second dose. Once the litres are known, which listing is worth opening is on the best pond clear page.
Common questions
How do I get litres from metres?
Multiply length by width by average depth, then by 1,000, with every measurement in metres. A 3 m by 2 m pond at 0.6 m average depth is 3,600 litres. Use that average, not the 1.2 m sump, or you plan a dose for water that is not there. A shelf at 0.4 m beside water at 0.8 m belongs in the average, or as its own box that you add.
Can I use Envii's 10 ml rate on Tetra or Blagdon?
No. The 10 ml per 1,000 litres figure is printed for Envii Pond Klear Xtra, on that listing and on Envii's page. Tetra CrystalWater and Blagdon Green Away are different liquids, and their listings do not print that rate. Tetra's UK page states 50 ml per 1,000 litres, which is the manufacturer page, not the Amazon text. Blagdon states a 5,000 litre bottle and leaves the millilitres off the listing.
Why did the water go cloudy after I dosed?
A clarifier can pull fine particles into visible clumps, so the pond often looks worse before it looks clearer. Tetra's UK page names temporary turbidity at its site rate. Milkier water the same evening is a reason to wait, not to pour a second bottle before that dose has had its own interval.
When do I repeat?
Follow the interval on the bottle you used, and do not borrow the next brand's calendar. Envii's Pond Klear page says every 7 days, and 6 to 8 weeks when the pond is very murky. Blagdon's FAQ, which is not the listing, allows a second dose the next morning only if the first partly worked. Still-green water tonight, on a weekly bacterial bottle, is that clock running, not a failed dose.
What if the pond is only 200 litres?
At Xtra's printed 10 ml per 1,000 litres, 200 litres is 2 ml. Many chambers will not show a mark that small, so you are guessing on a pond that cannot spare an extra millilitre. AquaDesign's 3 ml pipette is not a dose for that volume, because the listing prints no rate. A 5,000 litre Blagdon bottle is a pack size, not an instruction to tip a little in. If you cannot measure 2 ml, leave the cap on.
Related pages
Sources
Public UK and maker sources from the research digest, used for this page in October 2026. Prices, stars and review counts are from the six amazon.co.uk listings in this set, shelf date 19 October 2026. A fish-safety line is a listing claim, not an HSE approval. A 4.2-star row is not evidence that fish were unharmed.
- RHS, pond algae and blanket weed (retrieved 19 October 2026)
- Froglife, pond problems (retrieved 19 October 2026)
- HSE, COPR product types (retrieved 19 October 2026)
- Tetra UK, CrystalWater (retrieved 19 October 2026)
- Blagdon treatments FAQ (retrieved 19 October 2026)
- Envii Pond Klear Xtra (retrieved 19 October 2026)
- GOV.UK, great crested newts (retrieved 19 October 2026)
- That Pond Guy, calculating pond volume (retrieved 19 October 2026)