FAULT ISOLATION MANUAL · NUTRIENTS — PHOSPHATE

PO4-001 · Phosphate risingv1.0.2

Phosphate reads above the applicable upper boundary for your tank type and keeps climbing. This sheet isolates why, the way an aircraft maintenance manual would: confirm the reading, classify the nitrate picture, cross the method boundary, classify urgency for your tank, then act. Answer each numbered block and the sheet lights the path.

WHAT YOU'LL NEED

Your phosphate test kit or low-range checker (plus your ICP result or a second method)
A nitrate test kit
TDS readings from your RODI unit, if you run one
Salt mix, mixing container, and the water-change calculator
Your tank 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 your phosphate reading above the applicable upper boundary for your tank type, above 0.10 ppm (mixed reef) or above 0.05 ppm (SPS-dominant)? (Note: Some methods report phosphate as phosphorus (P), while this Manual uses phosphate as PO₄. Confirm the reporting basis before entering a value. PO4 is approximately 3.066 times P.)
YES → block 3 · NO → block 2

Block 2 — PO4-001 NOT ACTIVE (Why this procedure stopped: Your confirmed phosphate does not meet this procedure's high-phosphate entry condition. PO4-001 makes no determination about whether lower phosphate is appropriate for your aquarium. If phosphate is undetectable or repeatedly bottoming out, that condition is covered by PO4-002 when it is released.)
END — NO FAULT

Block 3 — Confirm the reading before acting on it. First, repeat the same test you already used (same kit, fresh sample, careful technique) to rule out a handling error. If you can, corroborate with your ICP result or another appropriate method. Express every result as PO₄ before comparing. Do all confirmed results agree that phosphate is above the applicable upper boundary for your tank type?
YES → block 5 · NO → block 4

Block 4 — Your results do not agree, or the repeat did not confirm the high reading. Do not average disagreeing methods and do not act on the higher number to be safe: both paths treat noise as signal. Retest carefully; if an ICP result and a hobby kit still disagree after a careful repeat, escalate with both results and the kit's brand, age, and reporting basis (PO₄ vs P). Run this procedure again once your methods agree.
END — ESCALATE RETEST

Block 5 — Does your most recent ICP result or nitrate test show nitrate at zero, or below the reporting limit?
YES → block 6 · NO → block 8

Block 6 — Confirm with a second, appropriate nitrate measurement: a different kit, or your ICP result if a hobby kit read zero. Does nitrate remain undetectable?
YES → block 7 · NO → block 8

Block 7 — Phosphate is confirmed high while nitrate is confirmed undetectable. Escalate to Decode with your full ICP result and both phosphate and nitrate test records. Do not intensify phosphate export, and do not dose nitrate based on this procedure. (Why this procedure stopped: This procedure cannot safely tell whether your tank is genuinely starved of nitrogen or whether the measurement is at its limit; and pushing phosphate export harder in either case can harm corals: research on reef corals shows skewed nutrient availability can worsen coral condition and bleaching susceptibility.)
END — ESCALATE DECODE

Block 8 — Are you actively running chemical phosphate removal: GFO or other phosphate-binding media, or lanthanum chloride dosing?
YES → block 9 · NO → block 12

Block 9 — Is that program fully documented: known product, amount in service or dose, the dates it went into service, and a dated log of how phosphate has responded?
YES → block 11 · NO → block 10

Block 10 — This procedure cannot safely advise you while an unmeasured chemical phosphate-removal program is running. Document the program fully (product, amount, dates, dated test results), then run this procedure again. (Why this procedure stopped: Isolating a phosphate source around an unquantified removal program is unsafe without knowing the product, the amount in service, when it went in, and how phosphate has responded so far. This is a coverage gap, not a recommendation to start or stop chemical phosphate removal.)
END — UNSUPPORTED METHOD

Block 11 — Phosphate is confirmed rising while a documented chemical-removal program is already running. Escalate to Decode with your program log and full test history. Do not start, increase, replace, or dose GFO, binding media, or lanthanum based on this procedure. (Why this procedure stopped: Adjusting chemical phosphate removal (amounts, replacement, or schedules) is outside this procedure's boundary, and rapid chemical reduction can drop phosphate faster than corals tolerate. A rising reading on a documented program needs multi-parameter review, not a bigger reactor.)
END — ESCALATE DECODE

Block 12 — Is your tank SPS-dominant, mostly small-polyp stony corals, run lean?
YES → block 14 · NO → block 13

Block 13 — Is your confirmed phosphate 0.25 ppm or higher?
YES → block 15 · NO → block 21

Block 14 — Is your confirmed phosphate 0.20 ppm or higher?
YES → block 15 · NO → block 21

Block 15 — Plan the exchange before touching water. Open the water-change calculator, enter your current phosphate, your interim target, and your system volume, and record the proposed exchange size, including whether it is one change or a series. The safety checks that follow depend on knowing this size.
then → block 16

Block 16 — Check the replacement batch against the planned exchange: (1) test the batch for phosphate with a salt-water-appropriate method you have validated: no detectable phosphate; (2) match salinity and temperature to the tank; (3) record the tank's alkalinity and the batch's alkalinity, and work out where the planned exchange size would put the tank's alkalinity; (4) confirm the salt is fully dissolved and the batch fully mixed. Record all results.
then → block 17

Block 17 — Did the batch and plan pass every check: no detectable phosphate, salinity and temperature matched, salt fully dissolved and mixed, and the planned exchange keeps tank alkalinity inside the acceptable range for your tank type: 8–10 dKH (mixed reef) or 7–9 dKH (SPS-dominant)?
YES → block 20 · NO → block 18

Block 18 — Which check failed: did the replacement water itself show detectable phosphate?
YES → block 23 · NO → block 19

Block 19 — Fix the plan or the batch, not the tank. If the alkalinity projection failed, reduce or stage the exchange in the calculator and re-run the numbers, correct the batch, or choose a salt mix closer to your tank's parameters. If salinity, temperature, or mixing failed, re-match and let the batch dissolve and mix completely. Do not perform the exchange with a plan and batch that failed preflight: at critical phosphate the exchange is large, and a mismatched batch trades one emergency for another. If repeated attempts cannot produce a passing plan and batch, escalate to Decode with your recorded readings instead of performing an unsafe exchange. (Note: This check window is BioForge procedure policy, not a biological constant.) (Verify — 1 day, REPLACEMENT WATER: A freshly planned exchange and prepared batch pass all preflight checks: no detectable phosphate by a salt-water-appropriate validated method, salinity and temperature matched, the planned exchange keeps tank alkalinity inside the applicable range, salt fully dissolved and fully mixed.)
verified resolved → done · problem continues → block 1

Block 20 — Bring phosphate out of the critical zone by executing the calculated plan with the batch that passed preflight. Follow the exchange size and count from the water-change calculator: if you re-plan between changes, re-run the calculator rather than guessing. Use a series of smaller calculated changes rather than one very large exchange when a large one would swing temperature, salinity, or alkalinity. Let each change mix completely, retest, and repeat until you are below the critical value for your tank type. Phosphate binds to rock and sand and can re-release after a change, so retest before judging the result: water changes remove phosphate that has already accumulated; they do not fix whatever is producing it. Once you are out of the critical zone, run this procedure again from the start to isolate the source. (Note: This check window is BioForge procedure policy for confirming the exchange worked, not a biological constant.) (Verify — 1 day, PHOSPHATE: After the changed water has fully mixed, a comparable phosphate test reads below the critical value for your tank type.)
verified resolved → done · problem continues → block 1

Block 21 — Test your replacement water, matching the method to the water: (1) RODI or top-off water, use a phosphate method appropriate for fresh water, and check your TDS readings; rising TDS after the DI stage is evidence the resin is exhausting. Do not apply a marine phosphate kit to pure RODI unless it is validated for fresh water. (2) Newly mixed salt water, fully dissolved, use the marine phosphate method you validated in the confirmation step. Record both readings and your TDS numbers.
then → block 22

Block 22 — Did either sample show detectable phosphate, or did TDS behavior show the RODI unit passing contaminants?
YES → block 23 · NO → block 24

Block 23 — Your replacement water is bringing phosphate in with it. Correct the component the evidence points to: if TDS rises after the DI stage, the resin is exhausting; if TDS rises before it, look at the membrane or prefilters; if RODI tests clean but the mixed salt water does not, the salt mix or mixing container is the entry point. Service or replace only what the readings and the manufacturer's guidance implicate: replacing everything at once hides which component failed. Do not add the contaminated water to the tank in the meantime. More than one contributor can exist: if tank phosphate does not begin to fall over your next comparable tests after the fix, run this procedure again. (Note: This check window is BioForge procedure policy, not a biological constant.) (Verify — 1 day, PHOSPHATE: Replacement and source water show no detectable phosphate, each tested with a method appropriate to its matrix, before being added to the aquarium.)
verified resolved → done · problem continues → block 1

Block 24 — Is your non-chemical nutrient export actually working? Check each one you run: skimmer producing normal skimmate volume and color; refugium macroalgae visibly growing, light on schedule; filter socks or floss changed on schedule.
YES → block 26 · NO → block 25

Block 25 — Restore the export path you found down: clean and re-tune the skimmer, restore refugium lighting and harvest overgrown macroalgae, resume the sock or floss schedule. Fix what is broken before adding anything new: this procedure does not direct chemical media changes. (Note: This check window is BioForge procedure policy, not a biological constant.) (Verify — 7 days, PHOSPHATE: The equipment's function is directly confirmed (skimmate production, new macroalgae growth, or a resumed sock schedule) AND a comparable phosphate test at day 7 is not higher than the test taken just after the repair.)
verified resolved → done · problem continues → block 1

Block 26 — Has phosphorus input risen, or is waste accumulating? Consider: feeding increased in amount or frequency, dry and frozen foods carry phosphate; thaw water from frozen food poured into the tank; new or larger fish; detritus built up in the sump, filter socks, or low-flow dead spots; an unnoticed loss decomposing somewhere.
YES → block 27 · NO → block 28

Block 27 — Reduce the excess you identified: return feeding to the earlier amount, drain and discard thaw water instead of pouring it in, siphon out the trapped detritus, remove the loss, or rehome livestock if stocking outran the system. Change one thing, write down what and when, and keep it changed: phosphate responds slowly, and rock and sand can buffer it against quick change, so reverting halfway makes the result unreadable. (Note: This check window is BioForge procedure policy, not a biological constant.) (Verify — 14 days, PHOSPHATE: The documented change was maintained for the full 14 days AND two comparable phosphate tests across that window show phosphate is no longer increasing.)
verified resolved → done · problem continues → block 1

Block 28 — Phosphate remains confirmed above the applicable upper boundary, but this procedure did not isolate the source. Escalate with the complete test history, tank profile, equipment list, feeding record, and the elimination trail from this procedure. (Why this procedure stopped: This procedure checked replacement-water contamination, export function, and phosphorus input, and none of them explained the confirmed rise: the remaining causes, including phosphate bound to rock and sand re-releasing into the water, need multi-parameter analysis, not another guess. Do not add a chemical removal method based on this result alone.)
END — ESCALATE DECODE