FAULT ISOLATION MANUAL · BASE PARAMETER — SALINITY

SAL-001 · Salinity driftingv1.0.3

Salinity reads outside your tank type's acceptable band. This sheet isolates why, the way an aircraft maintenance manual would: qualify the instrument, reproduce the reading, screen severity, classify the direction, then act. Answer each numbered block and the sheet lights the path.

WHAT YOU'LL NEED

A working tank-side salinity instrument (refractometer, digital salinity tester, or conductivity probe) with the calibration materials its manufacturer specifies
Your tank type (mixed reef or SPS-dominant)
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 — A salinity value, from your ICP report or any home reading, is outside the acceptable band for your tank type: 33–35.5 ppt for a mixed reef, 33.5–35.5 ppt for an SPS-dominant tank. Is that the case for your most recent value?
YES → block 3 · NO → block 2

Block 2 — Your reading is inside the acceptable band for your tank type. No salinity fault is open. (Why this procedure stopped: The entry condition, a reading outside the acceptable band for the declared tank type, is not met. Re-enter this fault if a future reading falls outside the band.)
END — NO FAULT

Block 3 — Do you have a working tank-side way to measure salinity (a refractometer, digital salinity tester, or conductivity probe) together with the calibration materials its manufacturer specifies?
YES → block 5 · NO → block 4

Block 4 — Salinity cannot be investigated without a qualified tank-side measurement. Obtain or repair a salinity instrument together with the calibration materials its manufacturer specifies, including a fresh, appropriate calibration or reference standard where the procedure requires one, then re-enter this fault. (Why this procedure stopped: Every branch of this investigation interprets a number that qualification validates. No corrective action is authorized on an unqualified reading.)
END — ESCALATE RETEST

Block 5 — Qualify your instrument, then take a fresh reading:
1. Calibrate the instrument exactly as its manufacturer's procedure specifies.
2. If it is a seawater-range refractometer and you are checking its accuracy near reef salinity, verify it against an appropriate seawater-range reference standard rather than assuming an RO/DI zero proves accuracy.
3. Take a fresh reading of tank water, at tank temperature.
4. Repeat the reading once to confirm it reproduces.
5. Record both readings and the calibration you performed.
then → block 6

Block 6 — Were you able to complete the calibration and obtain a fresh, reproduced tank-side reading?
YES → block 7 · NO → block 4

Block 7 — Is the fresh qualified reading outside the acceptable band for your tank type: below 33 or above 35.5 ppt (mixed reef), below 33.5 or above 35.5 ppt (SPS-dominant)?
YES → block 9 · NO → block 8

Block 8 — A fresh reading on a qualified instrument sits inside the acceptable band. The original out-of-band value was not reproduced. (Why this procedure stopped: The original out-of-band value was not reproduced on the qualified tank-side measurement. Keep the calibration and reading record. If the ICP result and qualified home result continue to disagree, do not average them; repeat the measurements and investigate the disagreement.)
END — NO FAULT

Block 9 — Is the fresh reading at or beyond the severe markers for your tank type: at or below 31 ppt (mixed) / 32 ppt (SPS), or at or above 37 ppt (mixed) / 36.5 ppt (SPS)?
YES → block 10 · NO → block 11

Block 10 — The fresh reading is at or beyond the severe markers for your tank type. A deviation this large is outside this procedure's staged corrections. (Why this procedure stopped: This is a coverage gap, not a verdict. Corrections of this size interact with temperature, oxygen, and livestock tolerance in ways this procedure does not model. Retest to confirm the reading. Do not use SAL-001's staged correction procedures for a reading at or beyond these markers.)
END — UNSUPPORTED METHOD

Block 11 — Is the fresh reading below the low edge of your band: under 33 ppt (mixed reef) or 33.5 ppt (SPS-dominant)?
YES → block 12 · NO → block 21

Block 12 — Has your auto-top-off or manual top-off routine changed recently, or do you suspect it is malfunctioning toward over-delivery: running longer than before, a new or adjusted pump, a moved level sensor, or a changed reservoir?
YES → block 13 · NO → block 16

Block 13 — Is the top-off system's prior working configuration documented in writing: a recorded setpoint, sensor position, pump output, or reservoir arrangement you could restore it to?
YES → block 14 · NO → block 18

Block 14 — Comparing the system against that written record, is it currently delivering more water than it did before, more than evaporation removes?
YES → block 15 · NO → block 16

Block 15 — Restore the top-off system, then correct the salinity.
First, restoration:
1. Return the top-off system to its documented configuration (the recorded setpoint, sensor position, pump output, and reservoir arrangement) so it no longer delivers more water than evaporation removes. Record what you changed and when.
2. Confirm the restored top-off stops at the correct water level before continuing.
Then, the bounded correction:
1. Never add dry salt directly to the aquarium or sump.
2. Prepare and completely dissolve saltwater separately.
3. Measure the prepared saltwater with the qualified instrument.
4. Its measured salinity may not exceed 35 ppt.
5. Substitute prepared saltwater only for water actually lost through evaporation. Never add extra volume merely to raise salinity.
6. If an ATO is being used during this correction, do not immediately fill an unrestricted full-size reservoir with saltwater. First confirm the top-off stops at the correct water level.
7. During correction, limit the saltwater supply available to the top-off system to no more than its documented normal short-term requirement, or perform the substitution manually. This prevents a renewed ATO failure from delivering an entire reservoir of saltwater.
8. Measure tank salinity at least daily with the qualified instrument.
9. As soon as the tank first enters its applicable band, stop saltwater substitution and return to ordinary RO/DI top-off.
10. Record the starting salinity, prepared-water salinity, each tank reading, the volume or top-off interval used, and when RO/DI top-off resumed. (Verify — 7 days, SALINITY: The 7-day window begins only after the tank first reads inside its applicable band, saltwater substitution has stopped, and ordinary RO/DI top-off has resumed. Every daily, same-time reading across the 7 days sits inside your tank type's acceptable band, 33–35.5 ppt (mixed reef) or 33.5–35.5 ppt (SPS-dominant), with no reading outside the band in either direction, and your written record is complete.)
verified resolved → done · problem continues → block 1

Block 16 — Separate from the top-off system: have you added water below the tank's salinity (plain RO/DI beyond what evaporation removed, a water-change batch mixed light, or a top-off reservoir that was supposed to be salted but wasn't)?
YES → block 17 · NO → block 20

Block 17 — Raise salinity by substituting your evaporation top-off, not by adding salt to the tank:
1. Never add dry salt directly to the aquarium or sump.
2. Prepare and completely dissolve saltwater separately.
3. Measure the prepared saltwater with the qualified instrument.
4. Its measured salinity may not exceed 35 ppt.
5. Substitute prepared saltwater only for water actually lost through evaporation. Never add extra volume merely to raise salinity.
6. If an ATO is being used during this correction, do not immediately fill an unrestricted full-size reservoir with saltwater. First confirm the top-off stops at the correct water level.
7. During correction, limit the saltwater supply available to the top-off system to no more than its documented normal short-term requirement, or perform the substitution manually. This prevents a renewed ATO failure from delivering an entire reservoir of saltwater.
8. Measure tank salinity at least daily with the qualified instrument.
9. As soon as the tank first enters its applicable band, stop saltwater substitution and return to ordinary RO/DI top-off.
10. Record the starting salinity, prepared-water salinity, each tank reading, the volume or top-off interval used, and when RO/DI top-off resumed. (Verify — 7 days, SALINITY: The 7-day window begins only after the tank first reads inside its applicable band, saltwater substitution has stopped, and ordinary RO/DI top-off has resumed. Every daily, same-time reading across the 7 days sits inside your tank type's acceptable band, 33–35.5 ppt (mixed reef) or 33.5–35.5 ppt (SPS-dominant), with no reading outside the band in either direction, and your written record is complete.)
verified resolved → done · problem continues → block 1

Block 18 — Separate from the top-off system: have you added water below the tank's salinity (plain RO/DI beyond what evaporation removed, a water-change batch mixed light, or a top-off reservoir that was supposed to be salted but wasn't)?
YES → block 17 · NO → block 19

Block 19 — The top-off system's prior working state is not documented, so restoring it is not a supported step; there is nothing recorded to restore to. The rest of this investigation already continued past the top-off branch. Document the system's current configuration now, so any future fault has a record to work from. (Why this procedure stopped: Restoration to a claimed prior configuration requires a written record of that configuration. This seals only the restoration step: the water-source causes were still checked on the way to this terminal.)
END — UNSUPPORTED METHOD

Block 20 — The reading is qualified and low, but neither the top-off system nor your water sources explain the dilution. Retest on the qualified instrument over the coming days and record the trend before intervening. (Why this procedure stopped: Correcting salinity without an isolated cause treats a symptom. If the reading stays low with no identified source of dilution, causes outside this procedure may remain.)
END — ESCALATE RETEST

Block 21 — Has your auto-top-off or manual top-off stopped or slowed recently, or do you suspect it is under-delivering: a clogged line, a failed pump, an empty reservoir, or a moved level sensor?
YES → block 22 · NO → block 25

Block 22 — Is the top-off system's prior working configuration documented in writing: a recorded setpoint, sensor position, pump output, or reservoir arrangement you could restore it to?
YES → block 23 · NO → block 27

Block 23 — Comparing the system against that written record, is it currently delivering less water than it did before, less than evaporation removes?
YES → block 24 · NO → block 25

Block 24 — Restore the top-off system, then correct the salinity.
First, restoration:
1. Return the top-off system to its documented configuration (the recorded setpoint, sensor position, pump output, and reservoir arrangement) so it no longer delivers less water than evaporation removes. Record what you changed and when.
2. Confirm the restored top-off stops at the correct water level before continuing.
Then, the calculated dilution:
Lower salinity with the calculated dilution procedure in the BioForge calculator, mode 07 (Salinity drift from dosing): enter your tank volume and the fresh reading, and follow its staged withdrawal and RO/DI-refill volumes exactly, including its swing-staging guidance. Measure with your qualified instrument after each stage and record every reading.
This is a calculated salinity-correction procedure. Its RO/DI replacement intentionally does not match the aquarium's salinity; do not reuse it as a routine water-change method. Temperature and every unaffected replacement-water parameter must still be controlled. (Verify — 7 days, SALINITY: The 7-day window begins only after the final calculated dilution stage is complete and the tank first reads inside its applicable band. Every daily, same-time reading across the 7 days sits inside your tank type's acceptable band, 33–35.5 ppt (mixed reef) or 33.5–35.5 ppt (SPS-dominant), with no reading outside the band in either direction, and your written record is complete.)
verified resolved → done · problem continues → block 1

Block 25 — Separate from the top-off system: have you added water above the tank's salinity (topped off with saltwater instead of RO/DI, used a replacement batch mixed strong, or returned salt creep or brine to the tank)?
YES → block 26 · NO → block 28

Block 26 — Lower salinity with the calculated dilution procedure in the BioForge calculator, mode 07 (Salinity drift from dosing): enter your tank volume and the fresh reading, and follow its staged withdrawal and RO/DI-refill volumes exactly, including its swing-staging guidance. Measure with your qualified instrument after each stage and record every reading.
This is a calculated salinity-correction procedure. Its RO/DI replacement intentionally does not match the aquarium's salinity; do not reuse it as a routine water-change method. Temperature and every unaffected replacement-water parameter must still be controlled. (Verify — 7 days, SALINITY: The 7-day window begins only after the final calculated dilution stage is complete and the tank first reads inside its applicable band. Every daily, same-time reading across the 7 days sits inside your tank type's acceptable band, 33–35.5 ppt (mixed reef) or 33.5–35.5 ppt (SPS-dominant), with no reading outside the band in either direction, and your written record is complete.)
verified resolved → done · problem continues → block 1

Block 27 — Separate from the top-off system: have you added water above the tank's salinity (topped off with saltwater instead of RO/DI, used a replacement batch mixed strong, or returned salt creep or brine to the tank)?
YES → block 26 · NO → block 19

Block 28 — The reading is qualified and high, but neither the top-off system nor your water sources explain the concentration. Retest on the qualified instrument over the coming days and record the trend before intervening. (Why this procedure stopped: Correcting salinity without an isolated cause treats a symptom. If the reading stays high with no identified source of concentration, causes outside this procedure may remain.)
END — ESCALATE RETEST