NO3:PO4-X 500 ml to 5 L — NoPox Nitrate and Phosphate Reducer for Reef Aquariums - Red Sea

NO3:PO4-X: biological nitrate and phosphate reduction

Red Sea NO3:PO4-X — NoPox to the hobby — is a complex of carbon sources and organically bound elements that lowers nitrate (NO3) and phosphate (PO4) together in a reef aquarium. Available here in 500 ml, 1 L and 5 L — pick your size right on this page.

How it works

Each carbon source in the formula feeds a different strain of micro-organism. With balanced enzymatic co-factors, those sources drive complete denitrification alongside phosphate reduction. The product is safe for fish, corals and microfauna.

The manufacturer's critical point: efficient protein skimming is essential to the safe use of NO3:PO4-X. Red Sea states that even a significant accidental overdose causes no irreversible damage as long as an adequately sized skimmer is running. If yours is borderline for the volume, sort that out first — see the RSK 600 Reefer Skimmer.

Official Red Sea daily dose (per 100 L / 25 gal)

Dosing is daily; NO3 and PO4 are measured weekly. A missed dose is never made up — simply resume at the current dose. At this size the dosing pump Red Sea recommends really earns its keep: the ReefDose 4 delivers the same dose to the millilitre, seven days a week.

What to measure with

NoPox is driven by test results, never by eye. For phosphate, the Hanna HI774 colorimeter reads 0.00 to 0.90 ppm and returns a number instead of a shade to interpret. For nitrate, the Salifert Nitrate test and the Red Sea Algae Control kit both do the job.

Available sizes

Red Sea lists four sizes: 100ml, 500ml, 1L and 5L. The 500ml is the trial size, the 1L is the established-tank size for continuous dosing, and the 5L targets very large systems. All three are selectable on this page.

Our advice

In 35 years in this trade, the question we hear most often is "I have algae, what do I do?" An algae problem is almost always a nutrient management problem: too much import, not enough export. You feed more than the system can process, and it builds up because nothing removes it. An aquarium is a closed vessel — nothing is lost, nothing is created. What you put in stays in.

The skimmer, the filtration, chemical media, phosphate removers, the refugium: all of that is what helps you export. But even with all that, when the skimmer isn't strong enough or the balance won't hold, NO3:PO4-X turbocharges your bacteria, which consume the nitrate and the phosphate.

It's a very good product, but be careful with it. You need to know the dosing, follow the instructions to the letter, and test your nitrate and phosphate constantly. This isn't a patch you apply once: when you start with it, you keep going, and you stay disciplined. But it works well.

Never dose blind. You adjust the dose based on what the tests tell you, not on impatience. For phosphate we prefer the Hanna testers — they're more reliable. For nitrate, the Red Sea is good, and we also like the Salifert.

The white veil: if you see a whitish veil appear, that's bacteria. Reduce the dose.

Who we steer away from it: the customer who doesn't want to look after their tank. Without follow-up, it's hard to succeed and hard to keep much livestock alive.

Official Red Sea videos

Frequently asked questions

What tank size is the 1L for?

It depends on the daily dose, not on volume alone. A 400 L Mixed Reef doses 8 ml per day per the official table, so a 1L bottle covers roughly four months at that rate. A Marine Fish system, which doses higher, goes through it faster.

Is NoPox safe for fish and corals?

Red Sea states the product is safe for fish, corals and microfauna, and that a significant accidental overdose causes no irreversible damage when an adequately sized skimmer is running.

How often should I test?

The manufacturer has you dose daily and measure NO3 and PO4 weekly.

Can I run it through a dosing pump?

Yes — Red Sea itself recommends a dosing pump for consistent daily dosing.

Manufacturer's official page