FAULT ISOLATION MANUAL · NUTRIENTS — PHOSPHATE

PO4-002 · Phosphate undetectablev1.1.1

Phosphate reads below your method's reporting capability, or keeps bottoming out after previously measurable results. This sheet isolates why, the way an aircraft maintenance manual would: qualify the method, confirm on a fresh sample, classify the nitrate picture, then walk each removable cause inside its own boundary. Answer each numbered block and the sheet lights the path.

WHAT YOU'LL NEED

Your marine low-range phosphate or phosphorus test method, with the manufacturer's instructions
A nitrate test kit
Your ICP result, if you have one (context, not a substitute for a fresh test)
Records of any binding media, lanthanum, carbon-dosing, or refugium/scrubber program you run
Your feeding log and a tank log (paper, spreadsheet, or BioForge account journal)

JavaScript is off, so the interactive sheet can't run — the complete printed logic is below. Start at block 1 and follow the YES/NO links. Nothing about your tank is inferred or stored.

Block 1 — Is phosphate non-detecting: has your most recent properly performed marine low-range phosphate test read below the method's reporting capability, or has it repeatedly bottomed out after previously measurable results? (Note: Repeatedly bottoming out means two consecutive non-detecting results on different days, using the same properly operated marine low-range method, after phosphate was previously measurable with that method. A single displayed zero may enter this confirmation sequence, but it cannot establish the repeated pattern by itself.)
YES → block 3 · NO → block 2

Block 2 — PO4-002 NOT ACTIVE — your phosphate is measurable. This sheet covers phosphate that is undetectable, below the selected method's reporting capability, or repeatedly bottoming out after previously measurable results. Return to the Manual index. (Why this procedure stopped: A measurable phosphate result does not meet the entry condition for this sheet: phosphate undetectable, below the selected method's reporting capability, or repeatedly bottoming out after previously measurable results. This procedure draws no conclusion about whether a measurable value is right for your tank.)
END — NO FAULT

Block 3 — Is your test method qualified for this decision: a marine low-range phosphate or phosphorus method, operated exactly per the manufacturer's procedure, with the reporting basis recorded (phosphorus P or phosphate PO₄; PO4 is approximately 3.066 times P)? (Note: Display resolution alone does not qualify a method. A displayed 0.00 is a non-detecting result, not proof that phosphate is absent; and an accuracy specification is not a detection limit. An ICP phosphorus result and a fresh colorimetric orthophosphate result may differ in reporting basis, phosphorus fraction, sample age, preparation, and method capability. Treat ICP as context unless the laboratory's analyte definition and handling procedure establish direct comparability.)
YES → block 5 · NO → block 4

Block 4 — UNSUPPORTED METHOD — this procedure needs a qualified marine low-range phosphate or phosphorus method operated per its manufacturer's instructions, with the reporting basis recorded. Obtain or properly operate such a method, then run this procedure again from the start. (Why this procedure stopped: The selected method cannot report phosphate at the level this decision requires, so the Manual cannot qualify its readings. This is a coverage gap in the procedure, not a judgment about your tank.)
END — UNSUPPORTED METHOD

Block 5 — Confirm with a fresh sample: repeat the same qualified method on a fresh sample on a different day, following the manufacturer's procedure exactly. Does it read non-detecting again? (Note: Two consecutive non-detecting results on different days with the same properly operated method establish the pattern this sheet acts on. Do not average results and do not act on the lower number to be safe.)
YES → block 10 · NO → block 6

Block 6 — Your fresh confirmation detected phosphate. Do your qualified results disagree with each other: non-detecting one day, clearly measurable the next, beyond what sample handling explains? (Note: Disagreement here means two properly performed, qualified results that conflict beyond what sample age, handling, or preparation explains. Handle it as a retest condition: do not average the numbers and do not pick one to act on.)
YES → block 7 · NO → block 8

Block 7 — Qualified methods disagree. Do not average them and do not act on either number. Retest with careful technique (fresh samples, the manufacturer's exact procedure, reporting basis recorded) until two properly performed results agree, then run this procedure again from the start.
END — ESCALATE RETEST

Block 8 — Is the detected reading above the applicable upper boundary for your tank type, above 0.10 ppm PO₄ (mixed reef) or above 0.05 ppm PO₄ (SPS-dominant)?
YES → block 9 · NO → block 2

Block 9 — PHOSPHATE HIGH — a confirmed reading above the upper boundary for your tank type is a rising-phosphate condition, which PO4-001 owns. Never repeat a phosphate-raising action against a high reading. (Why this procedure stopped: This sheet exists to restore detectable phosphate, so its actions permit phosphate to rise. A reading already above your tank type's upper boundary belongs to PO4-001 (phosphate rising); continuing here would point a raising procedure at a high result.)
END — NO FAULT

Block 10 — Classify nitrate before any intervention: is your current, properly performed nitrate result above the applicable upper boundary, above 15 ppm NO₃ (mixed reef) or above 8 ppm NO₃ (SPS-dominant)?
YES → block 11 · NO → block 19

Block 11 — Record this state in your tank log (paper, spreadsheet, or BioForge account journal): write "confirmed high-nitrate / non-detecting-phosphate imbalance" with today's date and both readings. The exact nitrate value you record now is the pre-intervention benchmark that later verification checks against. This is a recorded condition, not an emergency: it sets no deadline and skips nothing. Continue to the cause inventory.
then → block 12

Block 12 — Is phosphate-binding media in use right now: GFO-class or other binding media actively running on this system?
YES → block 22 · NO → block 13

Block 13 — Is lanthanum chloride being dosed on this system in any form?
YES → block 14 · NO → block 15

Block 14 — Can the lanthanum program be identified: the product, where it is added, and roughly when doses occur?
YES → block 25 · NO → block 26

Block 15 — Is a carbon-dosing program running on this system: vodka, vinegar, biopellets, or a commercial carbon source?
YES → block 16 · NO → block 17

Block 16 — Is the carbon program documented: a written product, dose, and schedule, including the program's own published adjustment for low-nutrient conditions?
YES → block 29 · NO → block 30

Block 17 — Is a refugium or algae scrubber exporting nutrients on this system?
YES → block 18 · NO → block 37

Block 18 — Does that refugium or scrubber have a documented, bounded adjustment procedure: specific written steps with defined limits, such as a stated photoperiod change, rather than a vague habit?
YES → block 33 · NO → block 34

Block 19 — Is nitrate also non-detecting: at or below your nitrate method's detection capability?
YES → block 20 · NO → block 21

Block 20 — Record this state in your tank log (paper, spreadsheet, or BioForge account journal): write "combined nitrate and phosphate depletion" with today's date and both readings. Continue to the cause inventory: this record travels with you and shapes the escalation reason if no removable cause is found.
then → block 21

Block 21 — Is phosphate-binding media in use right now: GFO-class or other binding media actively running on this system?
YES → block 22 · NO → block 23

Block 22 — Pause or remove only the binding media that is already running, following the media manufacturer's own instructions for taking it offline. Do not start new media, do not replace it with a different product, and change nothing else. Write down what was taken offline and when. (Note: This check window is BioForge procedure policy, not a biological constant.) (Verify — 3 days, PO4 + NO3: Phosphate reads detectable on the same qualified method AND PO₄ is at or below the applicable upper boundary for your tank type AND nitrate is freshly retested (if nitrate began above its applicable upper boundary, the fresh nitrate result is not higher than the recorded pre-intervention result; if nitrate began at or below its upper boundary, it remains at or below that boundary) AND the intervention and its timing are written down.)
verified resolved → done · problem continues → block 1

Block 23 — Is lanthanum chloride being dosed on this system in any form?
YES → block 24 · NO → block 27

Block 24 — Can the lanthanum program be identified: the product, where it is added, and roughly when doses occur?
YES → block 25 · NO → block 26

Block 25 — Stop adding further lanthanum doses. This procedure gives no amounts and no filtration steps: it only stops additional input from an identified program. Change nothing else, and write down when dosing stopped. (Note: This check window is BioForge procedure policy, not a biological constant.) (Verify — 3 days, PO4 + NO3: Phosphate reads detectable on the same qualified method AND PO₄ is at or below the applicable upper boundary for your tank type AND nitrate is freshly retested (if nitrate began above its applicable upper boundary, the fresh nitrate result is not higher than the recorded pre-intervention result; if nitrate began at or below its upper boundary, it remains at or below that boundary) AND the intervention and its timing are written down.)
verified resolved → done · problem continues → block 1

Block 26 — UNSUPPORTED METHOD — lanthanum appears to be entering this system, but the program cannot be identified well enough to act on. Identify the product, the addition point, and the timing, then run this procedure again from the start. (Why this procedure stopped: An active lanthanum program that cannot be identified cannot be safely bounded: the Manual cannot bound a procedure it cannot identify. This is a coverage gap in the procedure, not a judgment about your tank.)
END — UNSUPPORTED METHOD

Block 27 — Is a carbon-dosing program running on this system: vodka, vinegar, biopellets, or a commercial carbon source?
YES → block 28 · NO → block 31

Block 28 — Is the carbon program documented: a written product, dose, and schedule, including the program's own published adjustment for low-nutrient conditions?
YES → block 29 · NO → block 30

Block 29 — Apply the carbon program's own documented low-nutrient adjustment, and only that adjustment. This procedure adds nothing to it: no dose sizes of its own, no schedule of its own. Change nothing else, and write down the adjustment and the date. (Note: This check window is BioForge procedure policy, not a biological constant.) (Verify — 7 days, PO4 + NO3: Phosphate reads detectable on the same qualified method AND PO₄ is at or below the applicable upper boundary for your tank type AND nitrate is freshly retested (if nitrate began above its applicable upper boundary, the fresh nitrate result is not higher than the recorded pre-intervention result; if nitrate began at or below its upper boundary, it remains at or below that boundary) AND the intervention and its timing are written down.)
verified resolved → done · problem continues → block 1

Block 30 — UNSUPPORTED METHOD — the carbon-dosing program is not documented well enough to adjust safely. Recover or write down the product, dose, schedule, and its own low-nutrient adjustment, then run this procedure again from the start. (Why this procedure stopped: A carbon-dosing program without documentation has no established adjustment this Manual can point to, and the Manual will not invent one. This is a coverage gap in the procedure, not a judgment about your tank.)
END — UNSUPPORTED METHOD

Block 31 — Is a refugium or algae scrubber exporting nutrients on this system?
YES → block 32 · NO → block 35

Block 32 — Does that refugium or scrubber have a documented, bounded adjustment procedure: specific written steps with defined limits, such as a stated photoperiod change, rather than a vague habit?
YES → block 33 · NO → block 34

Block 33 — Follow the documented bounded adjustment for your refugium or scrubber exactly as written: its steps, its limits, nothing more. This procedure adds no steps of its own. Change nothing else, and write down what was adjusted and when. (Note: This check window is BioForge procedure policy, not a biological constant.) (Verify — 7 days, PO4 + NO3: Phosphate reads detectable on the same qualified method AND PO₄ is at or below the applicable upper boundary for your tank type AND nitrate is freshly retested (if nitrate began above its applicable upper boundary, the fresh nitrate result is not higher than the recorded pre-intervention result; if nitrate began at or below its upper boundary, it remains at or below that boundary) AND the intervention and its timing are written down.)
verified resolved → done · problem continues → block 1

Block 34 — UNSUPPORTED METHOD — your refugium or algae scrubber has no documented, bounded adjustment procedure. Write one down with specific steps and defined limits before adjusting anything, then run this procedure again from the start. (Why this procedure stopped: A refugium or scrubber without a documented bounded adjustment cannot be adjusted safely from here: the Manual cannot bound a procedure that has no defined limits. This is a coverage gap in the procedure, not a judgment about your tank.)
END — UNSUPPORTED METHOD

Block 35 — Was feeding or nutrient input recently reduced, with the previous level documented: a written record of what the input was before the reduction?
YES → block 36 · NO → block 37

Block 36 — Return feeding or nutrient input to the documented previous baseline, exactly there, never beyond it. This is a restoration of a recorded level, not a dosing substitute and not an increase past what you fed before. Change nothing else, and write down the restoration date. (Note: This check window is BioForge procedure policy, not a biological constant.) (Verify — 7 days, PO4 + NO3: Phosphate reads detectable on the same qualified method AND PO₄ is at or below the applicable upper boundary for your tank type AND nitrate is freshly retested (if nitrate began above its applicable upper boundary, the fresh nitrate result is not higher than the recorded pre-intervention result; if nitrate began at or below its upper boundary, it remains at or below that boundary) AND the intervention and its timing are written down.)
verified resolved → done · problem continues → block 1

Block 37 — Phosphate remains non-detecting after the bounded causes were addressed or ruled out. Decode is available as a separate step if you want a review of the full picture: bring your complete phosphate and nitrate history including reporting basis, your equipment and dosing record, and your tank log entries from this procedure. Do not start a chemical phosphate addition based on this procedure. (Why this procedure stopped: Any recorded state travels with this escalation: a confirmed high-nitrate / non-detecting-phosphate imbalance, a combined nitrate-and-phosphate depletion, or confirmed non-detection with no bounded removable cause. This procedure did not isolate an existing phosphate-removal method or a documented recent input reduction that it can safely reverse. Other causes may remain outside this tree. Direct chemical phosphate addition is also outside PO4-002 v1: it deliberately provides no product, no amount, no target dose, and no pacing constant, because nutrient-limited systems can carry lowered bleaching thresholds and dosing them is not a guess this procedure will underwrite.)
END — ESCALATE DECODE