Guides
Nutrients · Guide

Are zero nitrates and phosphates bad?

Sourced from published reef chemistry · 4 min read

Short answer: yes. In a reef tank, zero nitrate and zero phosphate is a problem, not a goal. Corals need some nutrients to live, and driving both to the floor is the classic setup for pest dinoflagellates and pale, starved coral. Aim for nitrate around 5–50 ppm and phosphate around 0.06–0.3 ppm — and never chase both to zero.

"Zero is clean" is an old myth

It's easy to assume that if some nutrients are bad, none must be best. Reef tanks don't work that way. Corals and their symbiotic algae feed on nitrogen and phosphorus — pull those to zero and you starve them. The visible result is coral that goes pale or washed-out, because a starved coral can't hold its colour. Natural reef water is very low in nutrients, but a closed tank isn't the open ocean: it needs a small, steady supply, not a desert.

The dinoflagellate connection

This is the one that catches people. When nitrate and phosphate both bottom out, the ordinary algae and bacteria that normally compete for space get starved back — and dinoflagellates, which can scrape by on almost nothing, move into the empty space. The result is the brown, snotty, bubble-filled strings reefers dread, and a dino outbreak is notoriously hard to reverse once it takes hold. Keeping a measurable amount of nitrate and phosphate in the water is one of the simplest ways to avoid ever starting one.

The healthy ranges

  • Nitrate: 5–50 ppm.
  • Phosphate: 0.06–0.3 ppm.

Both well above natural seawater, on purpose. As with everything else in a reef, steady beats chasing a number.

What to do if you're too low

If your nitrate or phosphate reads at or near zero:

  • Feed more. More food is the most natural way to raise nutrients — often the whole fix.
  • Ease off export. Scale back heavy skimming, carbon dosing, GFO or big water changes that are stripping nutrients out.
  • Dose them back up if needed. Nitrate and phosphate dosing products exist for exactly this; raise gradually and retest, don't overshoot.

Whichever you do, bring them up slowly and steadily — the goal is a stable, small supply, not a spike.

Frequently asked

Is zero nitrate good in a reef tank?
No. Aim for around 5–50 ppm. Zero starves coral and invites dinoflagellates.
Is zero phosphate bad?
Yes. Aim for around 0.06–0.3 ppm. Too-low phosphate produces pale coral and, with low nitrate, dinoflagellates.
Why do my corals look pale?
Often nutrients that are too low. Starved coral can't hold colour — check nitrate and phosphate before anything else.
Can low nutrients cause dinoflagellates?
Yes. When nitrate and phosphate both bottom out, dinoflagellates outcompete the starved organisms that would normally crowd them out.

Reef Stability tracks nitrate and phosphate against these ranges and warns you when both are drifting toward the floor — the pattern that precedes a dino outbreak — so you can feed a little more before it starts, not after.

Coming soon to the App Store
Sources: Randy Holmes-Farley, Optimal Parameters for a Coral Reef Aquarium (recommended nutrient ranges; low-nutrient dinoflagellate and coral-colour risk).