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    ULNS and Zeovit: ultra-low nutrient reef methods

    Push nitrate and phosphate close to zero for pale, pastel SPS colour. It works for skilled keepers with the right corals, but it leaves little margin, and the trend since about 2015 has been away from it.

    Last checked . How we check

    Cost
    High
    Effort
    High
    Suits
    Experienced SPS keepers
    Risk
    Pale or starving corals, dinoflagellates

    How does it work?

    Red Sea defines an ultra-low nutrient regime with salinity 33 ppt, alkalinity 7 dKH, calcium 410 and magnesium 1220, and its 2011 colour targets put nitrate at 0.25 and phosphate at 0.02.

    Zeovit (Korallen-Zucht) runs zeolite media in a reactor (about 1 litre per 100 US gallons, replaced every 6 to 12 weeks, flow kept at or below about 100 US gallons an hour), with added bacteria, a carbon source, amino acid food, constant carbon and strong skimming. Guides give alkalinity of 6.5 to 7.5 and magnesium of 1250 to 1300 (typical, check).

    What can go wrong with ultra-low nutrients?

    BRS links near-zero nitrate and phosphate to pale corals and dinoflagellates. Fauna Marin, Triton, BRS and Reef Builders all now warn that corals need some nitrate and phosphate. Fauna Marin and Reef Builders cite a nitrate to phosphate ratio of about 100 to 1 as linked with good colour; the evidence is ICP surveys and observation, not controlled studies.

    How do I get started?

    1. Run a stable tank for at least a year first.
    2. Choose one system and follow it fully.
    3. Lower nutrients slowly and test both every few days.
    4. Back off at the first sign of paling or brown slime.

    What are the common mistakes?

    • Trying it on a new tank.
    • Mixing parts of two systems.
    • Reading zero on a hobby kit as success rather than a warning.

    Where do sources disagree?

    Where sources disagree
    TopicWhat sources sayOur reading
    Nutrients
    • ULNS and the 2004 chemistry table: near zero
    • Reef Builders 2023: nitrate 5 to 10, phosphate 0.05 to 0.1
    • BRS 2025: nitrate under 25, phosphate under 0.1, both above zero
    		For a first tank, keep both measurable. Ultra-low is an advanced choice.

    Sources

    1. Red Sea, Foundation testing and supplementing manual (v21a)Published 2021. Read 21 October 2026, read in full.
    2. Red Sea, Reef Care Program brochure (2011 print, hosted by BRS)Published 2011. Read 21 October 2026, read in full.
    3. Korallen-Zucht, Zeovit system (guide summaries read via retailers)Read 21 October 2026, search summary only.
    4. BRS, high versus low nutrientsPublished 25 August 2025. Read 21 October 2026, read in full.
    5. Fauna Marin knowledge base, phosphorus and phosphateRead 21 October 2026, read in full.
    6. Reef Builders, the role of nutrients in a reef tankPublished 22 July 2023. Read 21 October 2026, read in full.

    Figures from sources read as a search summary only are shown as typical figures: check them before you rely on them. Found a mistake? Tell us how to fix it.