Red Sea NO3:PO4-X 500ml
Pack size
500 mL, 1 L and 5 L
Cost per litre
Under 1c
Water type
Saltwater + Reef
Red Sea NO3:PO4-X 500ml
One capful a day starves nuisance algae without starving your fish. Red Sea NO3:PO4-X is a liquid carbon source that feeds the bacteria already living in your reef system, encouraging them to consume excess nitrate and phosphate straight out of the water column. This 500 mL bottle is the size to start with — enough to run a full conversion in a small-to-medium reef, or to confirm the product suits your tank before stepping up to the 1 L or 5 L size.
Key features
- Feeds your own bacteria — a blend of carbon sources, each favoured by a different naturally occurring bacterial strain, so nutrient reduction happens biologically rather than through media that needs replacing.
- Treats nitrate and phosphate together — one bottle addresses both nutrients that drive nuisance algae, instead of running separate products for each.
- Dosed by an exact chart, not guesswork — Red Sea publishes a daily dose in millilitres per 100 L, set by your current nitrate and phosphate reading.
- Under 1c per litre of tank water treated — even at Red Sea's top dosing rate, this 500 mL bottle works out to well under a cent for every litre it treats.
- Room-temperature storage — no refrigeration required; keep out of direct light.
Specifications
| Spec | Red Sea NO3:PO4-X 500 mL |
|---|---|
| Volume | 500 mL |
| Form | Liquid concentrate, dosed daily |
| Water type | Marine / reef |
| Litres treated at the conservative dosing rate | Approx. 16,650 L over the life of the bottle |
| Cost per litre of water treated | Under 1c per litre |
Dosing chart — Red Sea's published rates
Dose is set by your current nitrate and phosphate readings, not a flat daily amount. Test weekly while dosing and adjust as levels fall.
| Parameter | Current level | Daily dose |
|---|---|---|
| Phosphate (PO₄) | Below 0.04 ppm | 1 mL per 100 L |
| Phosphate (PO₄) | 0.04–0.2 ppm | 2 mL per 100 L |
| Phosphate (PO₄) | Above 0.2 ppm | 3 mL per 100 L |
| Nitrate (NO₃) | Below 1 ppm | 1 mL per 100 L |
| Nitrate (NO₃) | Above 1 ppm | 2 mL per 100 L |
Where both nutrients are elevated at once, follow Red Sea's full instructions on combining the two doses rather than simply adding them together.
Cost per litre — which size to buy
All three NO3:PO4-X sizes work out to under 1 cent per litre of tank water treated at Red Sea's top dosing rate, but the larger bottles stretch further per dollar. The 500 mL bottle is the right starting size if you're new to carbon dosing or run a smaller system.
| Size | Price | Approx. litres treated* | Cost per litre |
|---|---|---|---|
| 500 mL (this bottle) | $27.00 | ~16,650 L | Under 1c per litre |
| 1 L | $42.00 | ~33,300 L | Under 1c per litre |
| 5 L | $157.00 | ~166,650 L | Under 1c per litre |
*Calculated at Red Sea's top published dosing rate of 3 mL per 100 L per day — the conservative, lowest-yield case, used when phosphate reads above 0.2 ppm. At lower nutrient levels the same bottle treats considerably more water and lasts longer.
Suitable for, and not suitable for
- Suitable for established marine and reef aquariums running an efficient protein skimmer.
- Suitable for use alongside Red Sea's Algae Management program when converting a tank off phosphate- and nitrate-absorbing media.
- Not suitable for use at the same time as sulphur-based denitrators.
- Not a spot treatment — this product doses the whole system daily, not a single application.
Dosage and directions
Add daily to the sump, or to a high-flow area of the display if there's no sump — never dosed directly onto coral. If this is your first time carbon dosing, start at half the recommended rate for the first few days and watch skimmer output, which will increase as bacteria multiply. A dosing pump keeps the small daily volume consistent.
Care and maintenance
Test nitrate and phosphate weekly while dosing and adjust to the chart above. Keep the protein skimmer running efficiently — the bacteria this product feeds are exported largely through skimmate, so a skimmer sized to your system matters as much as the dose itself.
Safety
Reduce the dose by half if nitrate falls below 0.25 ppm, and don't increase the dose faster than the chart allows — overdosing a carbon source can crash dissolved oxygen. Red Sea recommends switching off any UV steriliser while dosing, since UV will kill the bacteria the product is feeding. Not for use in planted or shrimp-only systems.
Goes well with
- Red Sea Nutrients Control Multi Test Kit (NO3/PO4) — the weekly nitrate and phosphate test this dosing chart is based on.
- Red Sea Reefer Skimmer 300 — efficient skimming is what exports the nutrient-laden bacteria this product feeds.
Warranty and delivery
Backed by Red Sea's standard product warranty, in addition to your rights under Australian Consumer Law. A 500 mL bottle ships as a standard parcel.
Common questions
Is NO3:PO4-X reef safe?
Yes, when dosed according to the chart above. Overdosing any carbon source can affect dissolved oxygen, so start conservatively and increase gradually while watching your skimmer.
How long will a 500 mL bottle last?
At Red Sea's top dosing rate it treats roughly 16,650 L of tank water — for a 200 L system dosed daily at the highest rate, that's a little over four months. Most tanks use less than the top rate, so a bottle typically lasts longer.
Can I use NO3:PO4-X alongside GFO or nitrate-removing media?
Yes — Red Sea's Algae Management program is built around gradually removing absorption media while introducing this product. Follow Red Sea's published conversion schedule rather than removing media all at once.
Do I need a UV steriliser switched off?
Red Sea recommends turning off a UV steriliser while dosing, since it will kill the bacteria this product relies on to reduce nitrate and phosphate.
