Easy-Life Fosfo phosphorus fertiliser for aquarium plants
Regular price
$7.00
Regular price
Sale price
$7.00
Unit price
/
per
| Contenance | Price | Price per L | vs 250 ml |
|---|---|---|---|
| 250 ml | $7.00 | $28.00 | — |
| 500 ml | $11.00 | $22.00 | −21 % |
Fosfo is a liquid fertiliser from Easy Life that supplies phosphorus to aquarium plants. It is a potassium phosphate solution, free of nitrate: 10 ml per 100 litres raises the PO4 by 1 mg/L.
It is dosed at 10 ml per 100 litres per week, and comes in 250 or 500 ml bottles.
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The summary
- Which bottle: 250 ml treats 2,500 L, 500 ml treats 5,000 L.
- What it provides: phosphate, in the form of potassium phosphate, with no nitrate.
- How to dose it: 10 ml per 100 L per week, according to the test.
- How to know: a PO4 test shows whether any needs to be added.
Phosphate without nitrate for heavily planted tanks, dosed according to a test
Fosfo, from the Easy Life brand, is a liquid fertiliser based on potassium phosphate, nitrate-free, intended for heavily planted aquariums where phosphate runs low. As 10 ml per 100 L raises PO4 by 1 mg/L, it is dosed according to a test, which allows phosphorus alone to be corrected.
Phosphorus is one of the three major elements that plants need, along with nitrogen and potassium. It plays a part in energy storage, root formation and the growth of young shoots. In a lightly stocked, heavily planted aquarium, the fish do not release enough of it: the plants use up the available phosphate and their growth slows. Fosfo lets you supply this phosphate in a directly absorbable form, without adding nitrate, and so correct one element at a time.
🧪 What's in the bottle
Fosfo is a monopotassium phosphate solution containing 0.8% phosphorus pentoxide. The calculation is simple: 10 ml in 100 litres raises the phosphate level by 1 mg/L, i.e. 1 ml per 10 litres. Each dose also provides a little potassium, around 0.4 mg/L, which your plants use. In a planted tank, the usual target is 0.5 to 1 mg/L of phosphate; up to 2 mg/L the level remains acceptable, but beyond that the surplus mainly benefits algae.
Phosphorus is only useful when it comes with the other elements. A plant that lacks nitrogen, potassium or iron will not benefit from a surplus of phosphate, which then remains available to the algae. This is why Fosfo is used in a test-guided fertilisation routine, element by element, rather than as a routine addition. This method adjusts nitrogen, phosphorus and potassium separately, then tops up with an iron and trace element fertiliser, which lets you correct exactly what is missing.
The nitrate test to balance the two
Adding phosphate only gives results if nitrogen keeps pace. The nitrate drop test, carried out at the same time as the phosphate test, shows you which of the two elements is really limiting growth. Nitrates at zero with phosphates present also favour cyanobacteria, and this double measurement helps you avoid that.
💧 Dosing based on a test
The reference dosage is 10 ml per 100 litres per week, after a test. In a 120-litre tank that reads 0.2 mg/L, you need to add 0.6 mg/L to reach about 0.8 mg/L, which is roughly 7 ml. Test again a few days later, as your plants take up phosphate at a rate that varies with the light and the season.
Add the dose preferably in the morning, when the lighting comes on, and pour it in near the filter outlet so that it disperses quickly. If you change part of the water every week, carry out the test after the water change: this is when the level is at its lowest and when the supplement is most useful. The 250 ml bottle treats 2,500 litres, which covers almost 6 months on a 100-litre tank at the weekly dose, while the 500 ml bottle suits a large tank or several aquariums.
🌱 In aquaponics
In aquaponics, phosphorus comes from the fish feed, and it is rarely lacking in a well-stocked system. It can, however, run short if your system is new or lightly stocked, or with demanding fruiting crops such as tomatoes. In a deep water culture grow bed, a level that is too low shows up as dark green leaves and delayed flowering. Measure it before making any correction: the article on choosing a fertiliser for aquaponics explains which supplements remain compatible with the fish.
Technical specifications
The essentials
- Nutrient supplied
- Phosphorus (PO4)
- Supply
- +1 mg/L of PO4 for 10 ml in 100 L
- Dosage
- 10 ml per 100 L per week, after testing
- Water
- Soft water, planted aquarium
To budget for separately
- Measurement
- Phosphate test
- Supplementary fertiliser
- A nitrogen fertiliser, to keep nitrogen and phosphorus in balance
In the box
- 1 bottle of Fosfo with dosing cap, 250 or 500 ml depending on the size chosen
Composition, supply and dosage as stated by the manufacturer Easy-Life, recorded on 13/10/2026. The potassium supplied is calculated from the formula for monopotassium phosphate.
Which bottle for your tank?
The same fertiliser in two sizes. What sets them apart is the volume treated.
250 or 500 ml?
Answer one question and the table highlights the bottle that suits you.
| Volume treated (L) | Time needed for a 100 L tank | Price | |
|---|---|---|---|
| Recommended 250 mlYour choice | 2500 L | Around 6 months | $7.00 |
| 500 ml Your choice | 5000 L | Approximately 1 year | $11.00 |
250 mlRecommended
What the bottle treats
Volume treated (L)2500 L
Time needed for a 100 L tankAround 6 months
500 ml
What the bottle treats
Volume treated (L)5000 L
Time needed for a 100 L tankApproximately 1 year
Volumes and durations calculated on the basis of 10 ml per 100 L per week.
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Frequently asked questions
6 questions
6 key questions
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