diff --git a/cue-ios/CueIOS/AppState.swift b/cue-ios/CueIOS/AppState.swift
index ba5f712..b8f88aa 100644
--- a/cue-ios/CueIOS/AppState.swift
+++ b/cue-ios/CueIOS/AppState.swift
@@ -97,6 +97,10 @@ final class AppState {
     var calRs: Double? = nil
     var clFactor: Double? = nil
     var clCalKnownPpm: String = "5"
+    var phSlope: Double? = nil
+    var phOffset: Double? = nil
+    var phCalPoints: [(ph: Double, mV: Double)] = []
+    var phCalKnown: String = "7.00"
 
     // Clean
     var cleanV: String = "1200"
@@ -262,6 +266,11 @@ final class AppState {
         case .clFactor(let f):
             clFactor = Double(f)
             status = String(format: "Device Cl factor: %.6f", f)
+
+        case .phCal(let slope, let offset):
+            phSlope = Double(slope)
+            phOffset = Double(offset)
+            status = String(format: "pH cal: slope=%.4f offset=%.4f", slope, offset)
         }
     }
 
diff --git a/cue-ios/CueIOS/Models/LsvAnalysis.swift b/cue-ios/CueIOS/Models/LsvAnalysis.swift
index 357ab5f..745b055 100644
--- a/cue-ios/CueIOS/Models/LsvAnalysis.swift
+++ b/cue-ios/CueIOS/Models/LsvAnalysis.swift
@@ -59,6 +59,32 @@ func findExtrema(_ v: [Float], _ iSmooth: [Float], minProminence: Float) -> [(In
     }
 }
 
+/// Detect Q/HQ redox peak in the -100 to +600 mV window.
+/// Returns peak voltage in mV if found.
+func detectQhqPeak(_ points: [LsvPoint]) -> Float? {
+    if points.count < 5 { return nil }
+
+    let iVals = points.map { $0.iUa }
+    let vVals = points.map { $0.vMv }
+
+    let window = max(5, points.count / 50)
+    let smoothed = smoothLsv(iVals, window: window)
+
+    guard let iMin = smoothed.min(), let iMax = smoothed.max() else { return nil }
+    let prominence = (iMax - iMin) * 0.05
+
+    let extrema = findExtrema(vVals, smoothed, minProminence: prominence)
+
+    let candidates = extrema
+        .filter { $0.1 && vVals[$0.0] >= -100 && vVals[$0.0] <= 600 }
+        .max(by: { smoothed[$0.0] < smoothed[$1.0] })
+
+    if let (idx, _) = candidates {
+        return vVals[idx]
+    }
+    return nil
+}
+
 func detectLsvPeaks(_ points: [LsvPoint]) -> [LsvPeak] {
     if points.count < 5 { return [] }
 
diff --git a/cue-ios/CueIOS/Models/Protocol.swift b/cue-ios/CueIOS/Models/Protocol.swift
index 61f9958..8a97608 100644
--- a/cue-ios/CueIOS/Models/Protocol.swift
+++ b/cue-ios/CueIOS/Models/Protocol.swift
@@ -30,6 +30,7 @@ let RSP_REF_LP_RANGE: UInt8 = 0x21
 let RSP_REFS_DONE:    UInt8 = 0x22
 let RSP_REF_STATUS:   UInt8 = 0x23
 let RSP_CL_FACTOR:    UInt8 = 0x24
+let RSP_PH_CAL:       UInt8 = 0x25
 
 // Cue -> ESP32
 let CMD_SET_SWEEP:     UInt8 = 0x10
@@ -49,6 +50,8 @@ let CMD_SET_CELL_K:    UInt8 = 0x28
 let CMD_GET_CELL_K:    UInt8 = 0x29
 let CMD_SET_CL_FACTOR: UInt8 = 0x33
 let CMD_GET_CL_FACTOR: UInt8 = 0x34
+let CMD_SET_PH_CAL:    UInt8 = 0x35
+let CMD_GET_PH_CAL:    UInt8 = 0x36
 let CMD_START_REFS:    UInt8 = 0x30
 let CMD_GET_REFS:      UInt8 = 0x31
 let CMD_CLEAR_REFS:    UInt8 = 0x32
@@ -127,6 +130,7 @@ enum EisMessage {
     case refStatus(hasRefs: Bool)
     case cellK(Float)
     case clFactor(Float)
+    case phCal(slope: Float, offset: Float)
 }
 
 // MARK: - Response parser
@@ -261,6 +265,12 @@ func parseSysex(_ data: [UInt8]) -> EisMessage? {
     case RSP_CL_FACTOR where p.count >= 5:
         return .clFactor(decodeFloat(p, at: 0))
 
+    case RSP_PH_CAL where p.count >= 10:
+        return .phCal(
+            slope:  decodeFloat(p, at: 0),
+            offset: decodeFloat(p, at: 5)
+        )
+
     default:
         return nil
     }
@@ -389,3 +399,15 @@ func buildSysexSetClFactor(_ f: Float) -> [UInt8] {
 func buildSysexGetClFactor() -> [UInt8] {
     [0xF0, sysexMfr, CMD_GET_CL_FACTOR, 0xF7]
 }
+
+func buildSysexSetPhCal(_ slope: Float, _ offset: Float) -> [UInt8] {
+    var sx: [UInt8] = [0xF0, sysexMfr, CMD_SET_PH_CAL]
+    sx.append(contentsOf: encodeFloat(slope))
+    sx.append(contentsOf: encodeFloat(offset))
+    sx.append(0xF7)
+    return sx
+}
+
+func buildSysexGetPhCal() -> [UInt8] {
+    [0xF0, sysexMfr, CMD_GET_PH_CAL, 0xF7]
+}
diff --git a/cue-ios/CueIOS/Transport/UDPManager.swift b/cue-ios/CueIOS/Transport/UDPManager.swift
index 726792f..a228c02 100644
--- a/cue-ios/CueIOS/Transport/UDPManager.swift
+++ b/cue-ios/CueIOS/Transport/UDPManager.swift
@@ -96,6 +96,7 @@ final class UDPManager: @unchecked Sendable {
             send(buildSysexGetConfig())
             send(buildSysexGetCellK())
             send(buildSysexGetClFactor())
+            send(buildSysexGetPhCal())
             startTimers()
             receiveLoop()