Should Reef Nitrate and Phosphate Be Zero?

🔍 Fact check

“Nitrate and phosphate should be kept at zero in a reef tank.”— Older reef advice — the cleaner, the better

Verdict: Outdated

Corals feed on nutrients. Truly zero nitrate and phosphate starves corals, pales SPS colour, and invites dinoflagellates. The modern reef target is low but not zero — roughly nitrate 2 to 15 ppm and phosphate 0.03 to 0.10 ppm. The parameters that must read zero are ammonia and nitrite, not nutrients.

The evidence:

Nitrate is coral food. Truly zero nitrate starves corals, pales SPS, and invites dinoflagellates — the modern target is low but measurable, roughly 2 to 15 ppm (Coralkin parameter target chart, sourced to reef-chemistry references and Bulk Reef Supply nutrient work).
Phosphate is coral food too. Zero phosphate also drives dinoflagellates and pale, receding corals — keep it low, not absent, around 0.03 to 0.10 ppm (Coralkin parameter target chart).
Stability beats chasing an exact number. A steady low nutrient level is far better for corals than a tank swinging toward zero — especially for alkalinity, the parameter corals are most sensitive to (Bulk Reef Supply reef chemistry).
Ammonia and nitrite are the ones that must be zero. In a cycled marine tank both should read undetectable — anything above means an uncycled tank or something dead. Those are the true zero targets, not nutrients.

🐠 The short version: in a reef tank, nitrate and phosphate should be low, but not zero — roughly nitrate 2–15 ppm and phosphate 0.03–0.10 ppm. They are coral food. Chase them to zero and you get pale, hungry corals and, very often, a dinoflagellate outbreak. The only things that should read zero are ammonia and nitrite. “The cleaner the better” is outdated advice.

🔧 See every target in one place on the parameter target chart — with the honest ranges, not just “zero.”

Why this myth spreads

For years, reef advice was built around export: skimmers, GFO, water changes, “pull the nutrients out.” Nitrate and phosphate were treated as pure pollution, and zero felt like the finish line. It is an intuitive story — dirty water is bad, so no nutrients must be best — and it is baked into a lot of older articles and store advice.

The trouble is that a reef is not just fish in a box; it is a tank full of animals — the corals — that actually eat those nutrients. Strip them to nothing and you are not cleaning the tank, you are starving half its inhabitants.

What is actually true

Corals get some of their nutrition directly from dissolved nutrients and from feeding, so nitrate and phosphate are inputs, not just waste:

Zero nitrate starves corals and pales SPS. The colour “pop” people chase actually depends on a low but present nutrient level; bottom it out and colours go pale and washed-out, and growth slows.
Zero phosphate does the same and feeds dinoflagellates. Nutrient-starved water is exactly the niche dinoflagellates exploit, which is why so many dino outbreaks happen in tanks that were “too clean.”
The modern target is a low band, not zero: roughly nitrate 2–15 ppm and phosphate 0.03–0.10 ppm.

There is one important flip side: ammonia and nitrite genuinely should be zero. In a cycled tank both read undetectable, and anything above means the tank is not cycled, is overloaded, or has something decaying in it. That is where the “should be zero” instinct is correct — just not for nutrients.

What to do with this

Test for a low band, not zero. Aim for the ranges above and check them on the parameter target chart.
If nutrients read zero, raise them. Feed more, or ease off export (less skimming, less GFO, back off carbon dosing). Yes — sometimes you dose or feed nutrients up.
Prize stability over a perfect number. A steady low level beats a tank yo-yoing toward zero, and alkalinity in particular hates swings.
Keep ammonia and nitrite at zero. Those are the real undetectable-target parameters — the sign of a properly cycled tank.

Nutrient control in a reef is about balance, not eradication. Keep them low and steady, feed your corals, and let ammonia and nitrite be the only numbers you drive to zero.

Sources & further reading

Coralkin — Reef parameter target chart — every target range, sourced, including the low-but-not-zero nutrient bands.
Bulk Reef Supply — reef water chemistry and nutrient (nitrate/phosphate) management.
Coralkin — Dosing calculator — for the alkalinity, calcium and magnesium side of reef chemistry.

Common questions

What should nitrate and phosphate be in a reef tank?

Low, but not zero. A widely used target is nitrate around 2 to 15 ppm and phosphate around 0.03 to 0.10 ppm. Both are coral food — pushing them to zero starves corals and tends to trigger dinoflagellates. Stability at a low level matters more than hitting an exact figure.

My nitrate is zero — is that bad?

It can be. Undetectable nitrate often shows up alongside pale corals, poor growth, and dinoflagellate outbreaks. If you are reading zero, the fix is usually to feed more or ease off nutrient export (skimmer, GFO, carbon dosing) — yes, sometimes you deliberately raise nutrients.

Which parameters should actually read zero?

Ammonia and nitrite. In a properly cycled tank both should be undetectable, and anything above zero points to an uncycled or overloaded tank, or something dead in the system. Nitrate and phosphate are different — those you keep low, not absent.

Why do dinoflagellates appear in a very clean tank?

Dinoflagellates thrive when nitrate and phosphate bottom out, because they outcompete other life in nutrient-starved water. A common first step in beating them is to bring nutrients back up to a healthy low level rather than driving them further down.