FAULT ISOLATION MANUAL · CARBONATE SYSTEM — PH

PH-001 · pH chronically lowv1.0.1

pH keeps reading below your tank type's lower boundary at the same time of day. This sheet isolates why, the way an aircraft maintenance manual would: qualify the meter, exclude the high side, reproduce the condition on a fresh reading, classify fresh alkalinity both ways, check an established kalkwasser program's integrity, then run the aeration comparison to locate where excess CO₂ resides. Answer each numbered block and the sheet lights the path.

WHAT YOU'LL NEED

A pH meter or probe with fresh calibration buffers that bracket reef readings (typically pH 7 and pH 10)
An alkalinity test kit that is in date and stored per its instructions
Two clean containers and an airstone for the aeration comparison
Records of any kalkwasser program or calcium reactor you run
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 — Measured tank-side at about the same time of day, has pH read below the applicable lower boundary, 8.0 (mixed reef) / 8.1 (SPS-dominant), on three or more days? (Note: A single low reading does not establish a chronic condition. Readings also below 7.9 (mixed) / 8.0 (SPS) indicate increased severity; the procedure is the same.)
YES → block 3 · NO → block 2

Block 2 — PH-001 NOT ACTIVE (Why this procedure stopped: The entry condition is not met. Occasional low readings, or readings taken at varying times of day, do not establish a chronically low pH. Continue normal monitoring at a consistent time of day.)
END — NO FAULT

Block 3 — Is the meter or probe calibrated according to its manufacturer's instructions, using fresh buffers that bracket the expected reading (for reef water, typically pH 7 and pH 10)? (Note: ICP sample pH is not accepted as tank-pH evidence because the transported sample no longer shares the aquarium's gas-exchange conditions.)
YES → block 5 · NO → block 4

Block 4 — END — MEASUREMENT NOT QUALIFIED (Why this procedure stopped: Calibrate the meter or probe according to its manufacturer's instructions with fresh bracketing buffers, then re-enter this procedure with qualified readings.)
END — ESCALATE RETEST

Block 5 — Take a fresh tank-side pH reading now. Is it at or above the applicable high threshold, 8.5 (mixed reef) / 8.45 (SPS-dominant)?
YES → block 6 · NO → block 7

Block 6 — PH-001 NOT ACTIVE — HIGH-SIDE CONDITION OUTSIDE THIS PROCEDURE. (Why this procedure stopped: The fresh reading is at or above the applicable high threshold (8.5 mixed / 8.45 SPS). Do not apply low-pH corrections. High-side pH conditions are outside this procedure's coverage.)
END — UNSUPPORTED METHOD

Block 7 — Is that same fresh reading still below the applicable lower boundary, 8.0 (mixed reef) / 8.1 (SPS-dominant)?
YES → block 9 · NO → block 8

Block 8 — END — CONDITION NOT REPRODUCED ON QUALIFIED MEASUREMENT (Why this procedure stopped: The fresh qualified reading is no longer below the applicable lower boundary (8.0 mixed / 8.1 SPS) and is below the high threshold (8.5 mixed / 8.45 SPS). The chronic-low condition did not reproduce, so cause isolation from a currently normal reading is not performed. Resume same-time-of-day monitoring and re-enter this procedure if the repeated low pattern returns.)
END — ESCALATE RETEST

Block 9 — Measure alkalinity now, with a test kit that is in date and stored per its instructions. Is the result at or above the lower boundary of your tank type's alkalinity range?
YES → block 11 · NO → block 10

Block 10 — PH-001 NOT ACTIVE — ALKALINITY BELOW RANGE (Why this procedure stopped: Alkalinity is below your tank type's range. Correct that first: low pH at low alkalinity is an alkalinity fault. Re-evaluate pH after ALK-001 closes.)
END — NO FAULT

Block 11 — Using that same fresh alkalinity result: is it at or below the upper boundary of your tank type's alkalinity range?
YES → block 13 · NO → block 12

Block 12 — PH-001 NOT ACTIVE — ALKALINITY ABOVE RANGE (Why this procedure stopped: Alkalinity is above your tank type's range. Correct that first. Re-evaluate pH after ALK-002 closes.)
END — NO FAULT

Block 13 — Is a kalkwasser top-off program intended to be running on this system right now: one that was part of the tank's normal operation when pH was last normal?
YES → block 14 · NO → block 18

Block 14 — Is that program's operating state documented: a recorded mix strength, delivery rate, and schedule from when pH was normal?
YES → block 16 · NO → block 15

Block 15 — END — UNSUPPORTED METHOD — KALKWASSER PROGRAM UNDOCUMENTED (Why this procedure stopped: A kalkwasser program is intended to be active on this system, but its operating state (mix strength, delivery rate, and schedule) is not documented. The tank is running under an unverified dosing control, and this procedure does not diagnose around one or create or estimate a kalkwasser dose. Record the program's current operating state, then re-enter this procedure.)
END — UNSUPPORTED METHOD

Block 16 — Is the program confirmed stopped or delivering materially below its documented state: reservoir ran dry, top-off or dosing pump failed, or mix strength or schedule reduced?
YES → block 17 · NO → block 18

Block 17 — Restore the kalkwasser program to its documented prior operating state: the recorded mix strength, delivery rate, and schedule. Do not increase beyond the documented values, and do not start a new program. Write down what you restored and the date. (Note: This 7-day same-time check window and its protocol are BioForge procedure policy, not a biological constant. Short before/after comparisons (including the aeration test) may show whether gas exchange affects pH, but they do not by themselves close the fault: only the 7-day same-time pattern does.) (Verify — 7 days, PH + ALK: The repeated same-time pattern finishes inside the applicable target band, 8.0–8.4 (mixed reef) / 8.1–8.3 (SPS-dominant), AND no reading reaches the applicable high threshold (8.5 mixed / 8.45 SPS) AND alkalinity, freshly measured, remains within your tank type's band AND the intervention and its dates are written down.)
verified resolved → done · problem continues → block 1

Block 18 — Since pH was last normal, has anything reduced gas exchange: surface agitation turned down, a return pump or powerhead removed or failed, tight-fitting lids or covers added, or the skimmer's air intake restricted, relocated, or partially clogged?
YES → block 19 · NO → block 20

Block 19 — Restore the prior gas-exchange arrangement: return surface agitation and pump output to their previous settings, remove or vent added covers, and clear or reconnect the skimmer air intake as it was. Change nothing else, and write down what you restored and the date. (Note: This 7-day same-time check window and its protocol are BioForge procedure policy, not a biological constant. Short before/after comparisons (including the aeration test) may show whether gas exchange affects pH, but they do not by themselves close the fault: only the 7-day same-time pattern does.) (Verify — 7 days, PH + ALK: The repeated same-time pattern finishes inside the applicable target band, 8.0–8.4 (mixed reef) / 8.1–8.3 (SPS-dominant), AND no reading reaches the applicable high threshold (8.5 mixed / 8.45 SPS) AND alkalinity, freshly measured, remains within your tank type's band AND the intervention and its dates are written down.)
verified resolved → done · problem continues → block 1

Block 20 — Record the tank's current pH as the starting value. Fill two clean containers with tank water. Aerate one outdoors (or at a wide-open window) and one in the room where the tank sits, each with an airstone, for about an hour. Keep the two samples at reasonably similar temperatures: a large temperature difference distorts the comparison. Then measure the pH of both with the qualified meter and write down all three values. (Note: This comparison indicates where excess CO₂ resides. It is a diagnostic only: it does not by itself close the fault.)
then → block 21

Block 21 — Did the outdoor-aerated sample rise above the starting value by more than your meter's stated accuracy?
YES → block 23 · NO → block 22

Block 22 — END — NO CO₂ EXCESS INDICATED — RECONCILE MEASUREMENT AND ALKALINITY (Why this procedure stopped: Outdoor aeration did not raise the sample's pH by more than the meter's stated accuracy, so excess dissolved CO₂ is not indicated. Re-verify the meter's calibration and the alkalinity measurement before proceeding: reactor and kalkwasser isolation are not continued from this result.)
END — ESCALATE RETEST

Block 23 — Did the indoor-aerated sample also rise above the starting value by more than your meter's stated accuracy?
YES → block 30 · NO → block 24

Block 24 — Is a CO₂ scrubber already installed on the skimmer air intake?
YES → block 25 · NO → block 27

Block 25 — Is the scrubber media exhausted (color change per its manufacturer), or is its air path loose, bypassed, or disconnected?
YES → block 26 · NO → block 27

Block 26 — Replace the exhausted scrubber media with the same type, following the manufacturer's instructions, and restore the air path exactly as originally installed. Change nothing else, and write down what you replaced and the date. (Note: This 7-day same-time check window and its protocol are BioForge procedure policy, not a biological constant. Short before/after comparisons (including the aeration test) may show whether gas exchange affects pH, but they do not by themselves close the fault: only the 7-day same-time pattern does.) (Verify — 7 days, PH + ALK: The repeated same-time pattern finishes inside the applicable target band, 8.0–8.4 (mixed reef) / 8.1–8.3 (SPS-dominant), AND no reading reaches the applicable high threshold (8.5 mixed / 8.45 SPS) AND alkalinity, freshly measured, remains within your tank type's band AND the intervention and its dates are written down.)
verified resolved → done · problem continues → block 1

Block 27 — Can you increase fresh outdoor air reaching the tank room using what you already have: opening windows or doors on a schedule, or adjusting an existing HVAC fresh-air setting?
YES → block 28 · NO → block 29

Block 28 — Increase fresh outdoor air to the tank room using the means you already have: the window/door schedule or HVAC fresh-air setting you identified. Keep the change consistent through the verification window, and write down what you changed and the date. (Note: This 7-day same-time check window and its protocol are BioForge procedure policy, not a biological constant. Short before/after comparisons (including the aeration test) may show whether gas exchange affects pH, but they do not by themselves close the fault: only the 7-day same-time pattern does.) (Verify — 7 days, PH + ALK: The repeated same-time pattern finishes inside the applicable target band, 8.0–8.4 (mixed reef) / 8.1–8.3 (SPS-dominant), AND no reading reaches the applicable high threshold (8.5 mixed / 8.45 SPS) AND alkalinity, freshly measured, remains within your tank type's band AND the intervention and its dates are written down.)
verified resolved → done · problem continues → block 1

Block 29 — ROOM-AIR CO₂ SOURCE ISOLATED — CORRECTION OUTSIDE THIS PROCEDURE. (Why this procedure stopped: The aeration comparison indicates that room air is depressing tank pH, but the available correction would require ventilation or equipment changes beyond this procedure. PH-001 does not recommend purchasing equipment.)
END — UNSUPPORTED METHOD

Block 30 — Is a calcium reactor in use on this system?
YES → block 31 · NO → block 35

Block 31 — Has its operation changed since pH was last normal: effluent rate drifted, CO₂ solenoid sticking or stuck open, effluent entering the display without the prior degassing arrangement, or settings altered?
YES → block 32 · NO → block 35

Block 32 — Is the reactor's prior working operation documented: a written or logged effluent rate, bubble rate, and plumbing arrangement from when pH was normal?
YES → block 33 · NO → block 34

Block 33 — Restore the reactor to its documented prior operation: the recorded effluent rate, bubble rate, and effluent/degassing arrangement. Do not tune to new settings, and write down what you restored and the date. (Note: Classified dose "raise" because restoring documented reactor operation is capable of increasing delivered alkalinity: not because every restoration necessarily raises the current dose. This 7-day same-time check window and its protocol are BioForge procedure policy, not a biological constant. Short before/after comparisons (including the aeration test) may show whether gas exchange affects pH, but they do not by themselves close the fault: only the 7-day same-time pattern does.) (Verify — 7 days, PH + ALK: The repeated same-time pattern finishes inside the applicable target band, 8.0–8.4 (mixed reef) / 8.1–8.3 (SPS-dominant), AND no reading reaches the applicable high threshold (8.5 mixed / 8.45 SPS) AND alkalinity, freshly measured, remains within your tank type's band AND the intervention and its dates are written down.)
verified resolved → done · problem continues → block 1

Block 34 — END — UNSUPPORTED METHOD — REACTOR OPERATION UNDOCUMENTED (Why this procedure stopped: The reactor's prior working operation is not documented. This procedure does not invent reactor settings or tune an undocumented system.)
END — UNSUPPORTED METHOD

Block 35 — Using only equipment you already have, can you improve gas exchange: raising surface agitation, redirecting return or powerhead flow toward the surface, venting or partially opening covers, or restoring the skimmer's full air draw?
YES → block 36 · NO → block 37

Block 36 — Improve gas exchange using only equipment you already have: raise surface agitation, redirect return or powerhead flow toward the surface, vent or partially open covers, and confirm the skimmer draws its full air supply. Do not purchase equipment. Write down what you adjusted and the date. (Note: This 7-day same-time check window and its protocol are BioForge procedure policy, not a biological constant. Short before/after comparisons (including the aeration test) may show whether gas exchange affects pH, but they do not by themselves close the fault: only the 7-day same-time pattern does.) (Verify — 7 days, PH + ALK: The repeated same-time pattern finishes inside the applicable target band, 8.0–8.4 (mixed reef) / 8.1–8.3 (SPS-dominant), AND no reading reaches the applicable high threshold (8.5 mixed / 8.45 SPS) AND alkalinity, freshly measured, remains within your tank type's band AND the intervention and its dates are written down.)
verified resolved → done · problem continues → block 1

Block 37 — END — CAUSE NOT ISOLATED (Why this procedure stopped: This procedure checked an established kalkwasser program's integrity, changed gas exchange, room-air CO₂, calcium-reactor operation, and gas-exchange optimization, and did not isolate a correctable cause. Other causes may remain outside this tree. A BioForge Decode review is available as a separate step if you choose it: bring the complete written history of readings, the aeration-test values, and interventions.)
END — ESCALATE DECODE