🎯 Nitrate Targets (NO₃⁻) — by System & Goal

Legend: ✅ ideal • ⚠️ watch • 🚫 avoid

🐠 Freshwater community (tetras, barbs, corys)

• ✅ ≤20 ppm
• ⚠️ 20–40 ppm (okay short-term for hardy fish)
• 🚫 >40 ppm (chronic stress ↑ disease)

🐟 Sensitive / wild-caught (discus, wild plecos, dwarf cichlids)

• ✅ ≤10–15 ppm (aim for ≤10 if you can)
• ⚠️ 15–25 ppm
• 🚫 >25 ppm

🛡️ Stingrays & other nitrate-sensitive big fish

• ✅ ≤10 ppm (many ray keepers run 5–10)
• ⚠️ 10–20 ppm
• 🚫 >20 ppm

🐣 Breeding & fry grow-outs

• ✅ ≤5–10 ppm
• ⚠️ 10–20 ppm (fertility/egg survival may drop)
• 🚫 >20 ppm

🌿 High-tech planted FW (CO₂, EI/lean dosing)

• Plants need nitrate: keep 5–20 ppm steady
• If algae blooms: check PO₄, K, CO₂ balance before cutting NO₃ too low

🌊 Marine

• Fish-only (FOWLR): ✅ ≤20–40 ppm
• Mixed reef/LPS: ✅ 5–10 ppm
• SPS-dominant: ✅ 2–5 ppm (ultra-low risk of “zero nitrate starvation”)

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🧠 Why these numbers matter (what nitrate does chronically)

• 🧪 Physiology: impairs osmoregulation and gill ion transport; raises metabolic/oxidative stress.
• 🩺 Immunity & disease: higher background mortality, slower healing; parasites/bacteria gain edge.
• 🧬 Reproduction: poorer gamete quality, egg/larval survival drops above ~20 ppm in many species.
• 🩸 Nitrite link: nitrate itself ≪ toxic than nitrite/ammonia, but dirty systems that run high NO₃ often have episodic NH₃/NO₂ spikes too.

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📏 Units & testing you can trust

• Many kits report mg/L as NO₃⁻. Some lab meters report mg/L as N (NO₃-N).
  • Convert: NO₃⁻ = 4.43 × NO₃-N
• ✅ Use a liquid kit/photometer; shake reagents vigorously (nitrate tests are notorious for under-mixing).
• 🧪 If reading off-scale, dilute the sample 1:1 or 1:4 with RO/DI and multiply back.
• 💧 Check tap water nitrate—if your source is 10–20 ppm, you’ll never hit low targets without RO/DI.

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🛠️ How to stay under target (stack these)

💧 Water changes (most reliable)

• If new water nitrate = N_new, current tank nitrate = N_now, target = N_target
  Required change fraction $f$f: $f=\frac{N_{now}-N_{target}}{N_{now}-N_{new}}$f=Nnow−NnewNnow−Ntarget (Example: N_now 60 → target 15, tap 5 ⇒ f = (60−15)/(60−5)=45/55=0.82 ⇒ 82% total change, done as 2–3 staggered changes to avoid swings in temp/TDS.)

🧼 Source & load control

• 🍽️ Right-size feeding (track grams/day; most tanks are overfed by 25–50%).
• 🧹 Mechanical export: prefilters, daily floss swaps; removes N before it mineralizes.
• ♻️ Deep-clean dead zones (sumps, hoses, under rocks) that leak nitrate back.

🌿 Assimilation: plants & algae

• FW: fast growers (hornwort, water sprite), floaters, pothos; give strong light + micronutrients so NO₃ is actually consumed.
• SW: refugium with chaeto or turf scrubber on reverse-light cycle.

🧫 Denitrification (true NO₃ removal)

• Anoxic media (sulfur denitrators, low-flow porous media) set up correctly.
• Carbon dosing (vodka/vinegar/NOPOX) for marine: powerful but monitor DO & skimmer—bacterial blooms can de-oxygenate water.

🚰 When source water has nitrate

• RO/DI + remineralization (FW) or salt mix (SW).
• Blend RO with tap to meet hardness while keeping NO₃ target reachable.

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🧮 Planning cheat-sheet (rules of thumb)

• 📉 Weekly drop needed to hold a setpoint:
  • If your system adds ~20 ppm/week, and your new water is ~0 ppm, a 50% weekly change holds you near ~10 ppm steady.
• 🐟 Stocking effect: doubling biomass roughly doubles weekly nitrate rise (same feeding style).
• 🌡️ Warm water → faster metabolism → faster NO₃ climb.
• 🧪 Trend beats snapshots: log ppm/week slope. If slope >5–10 ppm/week, add export capacity.

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🚦 Action thresholds to run by (freshwater)

• 0–10 ppm: ideal for wild/sensitive, breeding, rays.
• 10–20 ppm: good for most setups; keep stable.
• 20–40 ppm: serviceable for hardy fish; schedule larger/export upgrades.
• >40 ppm: corrective action—big changes in stages + add real export.

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🧯 Safe reduction protocol (when you’re high)

1. Stage large changes (e.g., 40% today, 40% tomorrow) to avoid temp/TDS swings.
2. Match temp/KH/GH closely; rays/discus are osmo-sensitive.
3. Boost aeration during big cleanups (detritus release can sap O₂).
4. Resume maintenance cadence based on your measured weekly nitrate slope.

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📋 Quick targets you can post in the fish room

• Rays/Discus/Wild Loricariids: ≤10 ppm
• General FW communities: ≤20–30 ppm (hard cap 40)
• Planted high-tech: 5–20 ppm steady (don’t “0-out” NO₃)
• Marine FOWLR: ≤20–40 ppm
• Reef: 2–10 ppm (system-specific; avoid 0)