diff --git a/api/internal/state/blocks.go b/api/internal/state/blocks.go
index 00c7ffe..598351b 100644
--- a/api/internal/state/blocks.go
+++ b/api/internal/state/blocks.go
@@ -23,6 +23,7 @@ type BlockRecord struct {
 	Source     string    `json:"source"` // "logmon" for now; "zmq" later
 	ShareDiff  float64   `json:"share_diff,omitempty"`
 	OrphanedAt time.Time `json:"orphaned_at,omitempty"`
+	Chain      string    `json:"chain,omitempty"` // "main", "test", "signet"
 }
 
 // IngestAttemptEvents counts "Possible/Submitting block solve" log
@@ -67,11 +68,20 @@ func (a *Aggregator) IngestBlockEvents(ctx context.Context, events <-chan logmon
 			if !ok {
 				return
 			}
+			// Stamp the chain name at the moment the block is seen so
+			// the reconcile loop can skip it if the node switches networks.
+			a.mu.RLock()
+			currentChain := ""
+			if a.snap.Chain != nil {
+				currentChain = a.snap.Chain.Chain
+			}
+			a.mu.RUnlock()
 			rec := BlockRecord{
 				Height:    ev.Height,
 				FoundAt:   ev.SeenAt,
 				Source:    "logmon",
 				ShareDiff: ev.ShareDiff,
+				Chain:     currentChain,
 			}
 			// Best-effort enrich with hash + coinbase reward via bitcoind.
 			// We look up the hash from height, then fetch the full block
@@ -101,6 +111,7 @@ func (a *Aggregator) IngestBlockEvents(ctx context.Context, events <-chan logmon
 					FoundAt:   rec.FoundAt,
 					Source:    rec.Source,
 					ShareDiff: rec.ShareDiff,
+					Chain:     rec.Chain,
 				})
 				if err != nil {
 					a.Log.Warn("block persist failed", "height", rec.Height, "err", err)
@@ -199,6 +210,18 @@ func (a *Aggregator) reconcileOnce(ctx context.Context) {
 	// matches our record. Don't bother with rows that are already
 	// orphaned — we won't un-orphan, since the network already
 	// chose another chain.
+	//
+	// Skip blocks whose recorded chain doesn't match the current
+	// bitcoind network — they were mined on a different node config
+	// (e.g. testnet) and cannot be checked against mainnet's tip.
+	// A mismatch here is a false positive, not a real reorg.
+	a.mu.RLock()
+	currentChain := ""
+	if a.snap.Chain != nil {
+		currentChain = a.snap.Chain.Chain
+	}
+	a.mu.RUnlock()
+
 	recent, err := a.Store.Recent(64)
 	if err != nil {
 		a.Log.Warn("reconcile: load recent failed", "err", err)
@@ -213,6 +236,13 @@ func (a *Aggregator) reconcileOnce(ctx context.Context) {
 		if b.FoundAt.Before(since) {
 			continue
 		}
+		// Both chain values must be known before we can compare them.
+		// Legacy rows (Chain=="") fall through so existing installs keep
+		// their reorg detection — there was no network switch before this
+		// feature landed.
+		if b.Chain != "" && currentChain != "" && b.Chain != currentChain {
+			continue
+		}
 		lookupCtx, cancel := context.WithTimeout(ctx, 3*time.Second)
 		canonical, herr := a.RPC.GetBlockHash(lookupCtx, b.Height)
 		cancel()
@@ -291,6 +321,7 @@ func (a *Aggregator) loadPersistedBlocks() {
 			Source:     r.Source,
 			ShareDiff:  r.ShareDiff,
 			OrphanedAt: r.OrphanedAt,
+			Chain:      r.Chain,
 		})
 	}
 	a.mu.Lock()
diff --git a/api/internal/store/blocks.go b/api/internal/store/blocks.go
index 4a35156..8057ef0 100644
--- a/api/internal/store/blocks.go
+++ b/api/internal/store/blocks.go
@@ -28,6 +28,7 @@ type Block struct {
 	Source     string
 	ShareDiff  float64
 	OrphanedAt time.Time // zero value = not orphaned
+	Chain      string    // "main", "test", "signet", or "" for legacy rows
 }
 
 const schema = `
@@ -38,7 +39,8 @@ CREATE TABLE IF NOT EXISTS blocks (
     found_at     INTEGER NOT NULL,
     source       TEXT NOT NULL DEFAULT '',
     share_diff   REAL NOT NULL DEFAULT 0,
-    orphaned_at  INTEGER NOT NULL DEFAULT 0
+    orphaned_at  INTEGER NOT NULL DEFAULT 0,
+    chain        TEXT NOT NULL DEFAULT ''
 );
 CREATE INDEX IF NOT EXISTS blocks_found_at_idx ON blocks(found_at);
 
@@ -83,6 +85,11 @@ func (s *BlockStore) migrate() error {
 			return fmt.Errorf("store: add orphaned_at: %w", err)
 		}
 	}
+	if !have["chain"] {
+		if _, err := s.db.Exec(`ALTER TABLE blocks ADD COLUMN chain TEXT NOT NULL DEFAULT ''`); err != nil {
+			return fmt.Errorf("store: add chain: %w", err)
+		}
+	}
 	return nil
 }
 
@@ -121,9 +128,9 @@ func (s *BlockStore) Close() error {
 // unnoticed.
 func (s *BlockStore) InsertBlock(b Block) (bool, error) {
 	res, err := s.db.Exec(
-		`INSERT OR IGNORE INTO blocks(height, hash, reward_btc, found_at, source, share_diff)
-		 VALUES (?, ?, ?, ?, ?, ?)`,
-		b.Height, b.Hash, b.RewardBT, b.FoundAt.Unix(), b.Source, b.ShareDiff,
+		`INSERT OR IGNORE INTO blocks(height, hash, reward_btc, found_at, source, share_diff, chain)
+		 VALUES (?, ?, ?, ?, ?, ?, ?)`,
+		b.Height, b.Hash, b.RewardBT, b.FoundAt.Unix(), b.Source, b.ShareDiff, b.Chain,
 	)
 	if err != nil {
 		return false, err
@@ -201,7 +208,7 @@ func (s *BlockStore) Recent(limit int) ([]Block, error) {
 		limit = 256
 	}
 	rows, err := s.db.Query(
-		`SELECT height, hash, reward_btc, found_at, source, share_diff, orphaned_at
+		`SELECT height, hash, reward_btc, found_at, source, share_diff, orphaned_at, chain
 		 FROM blocks ORDER BY height DESC LIMIT ?`,
 		limit,
 	)
@@ -213,7 +220,7 @@ func (s *BlockStore) Recent(limit int) ([]Block, error) {
 	for rows.Next() {
 		var b Block
 		var foundUnix, orphanedUnix int64
-		if err := rows.Scan(&b.Height, &b.Hash, &b.RewardBT, &foundUnix, &b.Source, &b.ShareDiff, &orphanedUnix); err != nil {
+		if err := rows.Scan(&b.Height, &b.Hash, &b.RewardBT, &foundUnix, &b.Source, &b.ShareDiff, &orphanedUnix, &b.Chain); err != nil {
 			return nil, err
 		}
 		b.FoundAt = time.Unix(foundUnix, 0).UTC()
@@ -234,7 +241,7 @@ func (s *BlockStore) Recent(limit int) ([]Block, error) {
 // retrying will keep failing.
 func (s *BlockStore) BlocksNeedingEnrichment(since time.Time) ([]Block, error) {
 	rows, err := s.db.Query(
-		`SELECT height, hash, reward_btc, found_at, source, share_diff, orphaned_at
+		`SELECT height, hash, reward_btc, found_at, source, share_diff, orphaned_at, chain
 		 FROM blocks
 		 WHERE found_at >= ? AND (hash = '' OR reward_btc = 0)
 		 ORDER BY height ASC`,
@@ -248,7 +255,7 @@ func (s *BlockStore) BlocksNeedingEnrichment(since time.Time) ([]Block, error) {
 	for rows.Next() {
 		var b Block
 		var foundUnix, orphanedUnix int64
-		if err := rows.Scan(&b.Height, &b.Hash, &b.RewardBT, &foundUnix, &b.Source, &b.ShareDiff, &orphanedUnix); err != nil {
+		if err := rows.Scan(&b.Height, &b.Hash, &b.RewardBT, &foundUnix, &b.Source, &b.ShareDiff, &orphanedUnix, &b.Chain); err != nil {
 			return nil, err
 		}
 		b.FoundAt = time.Unix(foundUnix, 0).UTC()
diff --git a/ui/src/lib/BlocksTable.svelte b/ui/src/lib/BlocksTable.svelte
index a1dd739..ae55c7b 100644
--- a/ui/src/lib/BlocksTable.svelte
+++ b/ui/src/lib/BlocksTable.svelte
@@ -10,6 +10,8 @@
   const explorerBase = $derived(
     explorerBaseFor(snap.data?.chain?.chain, snap.data?.mempool_base_url),
   );
+
+  const currentChain = $derived(snap.data?.chain?.chain ?? "");
 </script>
 
 <section class="card">
@@ -36,6 +38,9 @@
                 {#if b.orphaned_at}
                   <span class="orphan-tag" title="Reorged out of the canonical chain at {b.orphaned_at}">orphaned</span>
                 {/if}
+                {#if b.chain && currentChain && b.chain !== currentChain}
+                  <span class="chain-tag" title="Mined on {b.chain} — current node is {currentChain}">{b.chain}</span>
+                {/if}
               </td>
               <td class="hash-cell">
                 {#if b.hash}
@@ -121,6 +126,18 @@
     text-decoration: none;
     vertical-align: middle;
   }
+  .chain-tag {
+    display: inline-block;
+    margin-left: 0.4em;
+    padding: 0.05em 0.4em;
+    border-radius: 3px;
+    background: rgba(80, 160, 220, 0.15);
+    color: rgb(100, 170, 220);
+    font-size: 0.7em;
+    font-weight: 600;
+    text-decoration: none;
+    vertical-align: middle;
+  }
   .unit {
     color: var(--fg-dim);
     font-size: 0.75em;
diff --git a/ui/src/types.ts b/ui/src/types.ts
index 79ba898..f257504 100644
--- a/ui/src/types.ts
+++ b/ui/src/types.ts
@@ -98,6 +98,9 @@ export type BlockRecord = {
   // longer matches the canonical block at this height (network reorged
   // us out). UI renders these strikethrough.
   orphaned_at?: string; // RFC 3339, omitted when zero
+  // Bitcoin network the block was mined on ("main", "test", "signet").
+  // Absent for legacy rows recorded before this field was added.
+  chain?: string;
 };
 
 export type HashratePoint = {