diff --git a/CHANGELOG b/CHANGELOG
index b2a22aecf..661729ab0 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,6 @@
+1.6.X
+* New setting: lock_during_index
+
 1.6.1
 * fixed last_txs setting
 * added hashrate_units setting
diff --git a/UPGRADE b/UPGRADE
index af8eb0d45..813e936fe 100644
--- a/UPGRADE
+++ b/UPGRADE
@@ -1,5 +1,10 @@
 Note: All updates require the explorer to be restarted
 
+1.6.1 -> 1.6.X
+* Fix mismatching balances/sent/received, negative balances etc
+* Add new settings to settings.json (see settings.json.template)
+  * lock_during_index
+
 1.6.0 -> 1.6.1
 * Add new cryptsy_id and hashrate_units settings (see settings.json.template)
 * remove tmp/market.pid (if it exists)
diff --git a/app.js b/app.js
index 81dd91e5b..8f21a9292 100644
--- a/app.js
+++ b/app.js
@@ -120,6 +120,7 @@ app.set('youtube', settings.youtube);
 app.set('genesis_block', settings.genesis_block);
 app.set('index', settings.index);
 app.set('heavy', settings.heavy);
+app.set('lock_during_index', settings.lock_during_index);
 app.set('txcount', settings.txcount);
 app.set('nethash', settings.nethash);
 app.set('nethash_units', settings.nethash_units);
diff --git a/lib/database.js b/lib/database.js
index fd9bb2d65..9ac8fa42e 100644
--- a/lib/database.js
+++ b/lib/database.js
@@ -8,6 +8,7 @@ var mongoose = require('mongoose')
   , Heavy = require('../models/heavy')
   , lib = require('./explorer')
   , settings = require('./settings')
+  , fs = require('fs')
   , poloniex = require('./markets/poloniex')
   , bittrex = require('./markets/bittrex')
   , bleutrade = require('./markets/bleutrade')
@@ -230,6 +231,56 @@ function get_market_data(market, cb) {
   }
 }
 
+function create_lock(cb) {
+  if (settings.lock_during_index == true) {
+    database = 'db_index';
+    var fname = './tmp/' + database + '.pid';
+    fs.appendFile(fname, process.pid, function (err) {
+      if (err) {
+        console.log("Error: unable to create %s", fname);
+        process.exit(1);
+      } else {
+        return cb();
+      }
+    });
+  } else {
+    return cb();
+  }
+}
+
+function remove_lock(cb) {
+  if (settings.lock_during_index == true) {
+    database = 'db_index';
+    var fname = './tmp/' + database + '.pid';
+    fs.unlink(fname, function (err){
+      if(err) {
+        console.log("unable to remove lock: %s", fname);
+        process.exit(1);
+      } else {
+        return cb();
+      }
+    });
+  } else {
+    return cb();
+  }
+}
+
+function is_locked(cb) {
+  if (settings.lock_during_index == true) {
+    database = 'db_index';
+    var fname = './tmp/' + database + '.pid';
+    fs.exists(fname, function (exists){
+      if(exists) {
+        return cb(true);
+      } else {
+        return cb(false);
+      }
+    });
+  } else {
+    return cb(false);
+  }
+}
+
 module.exports = {
   // initialize DB
   connect: function(database, cb) {
@@ -338,29 +389,43 @@ module.exports = {
   },
 
   create_tx: function(txid, cb) {
-    save_tx(txid, function(err){
-      if (err) {
-        return cb(err);
-      } else {
-        //console.log('tx stored: %s', txid);
+    is_locked(function (exists) {
+      if (exists) {
+        console.log("db_index lock file exists...");
         return cb();
+      } else {
+        save_tx(txid, function(err){
+          if (err) {
+            return cb(err);
+          } else {
+            //console.log('tx stored: %s', txid);
+            return cb();
+          }
+        });
       }
     });
   },
 
   create_txs: function(block, cb) {
-    lib.syncLoop(block.tx.length, function (loop) {
-      var i = loop.iteration();
-      save_tx(block.tx[i], function(err){
-        if (err) {
-          loop.next();
-        } else {
-          //console.log('tx stored: %s', block.tx[i]);
-          loop.next();
-        }
-      });
-    }, function(){
-      return cb();
+    is_locked(function (exists) {
+      if (exists) {
+        console.log("db_index lock file exists...");
+        return cb();
+      } else {
+        lib.syncLoop(block.tx.length, function (loop) {
+          var i = loop.iteration();
+          save_tx(block.tx[i], function(err){
+            if (err) {
+              loop.next();
+            } else {
+              //console.log('tx stored: %s', block.tx[i]);
+              loop.next();
+            }
+          });
+        }, function(){
+          return cb();
+        });
+      }
     });
   },
 
@@ -619,64 +684,75 @@ module.exports = {
 
   // updates tx, address & richlist db's; called by sync.js
   update_tx_db: function(coin, start, end, timeout, cb) {
-    var complete = false;
-    lib.syncLoop((end - start) + 1, function (loop) {
-      var x = loop.iteration();
-      if (x % 5000 === 0) {
-        Tx.find({}).where('blockindex').lt(start + x).sort({timestamp: 'desc'}).limit(settings.index.last_txs).exec(function(err, txs){
-          Stats.update({coin: coin}, {
-            last: start + x - 1,
-            last_txs: '' //not used anymore left to clear out existing objects
-          }, function() {});
-        });
-      }
-      lib.get_blockhash(start + x, function(blockhash){
-        if (blockhash) {
-          lib.get_block(blockhash, function(block) {
-            if (block) {
-              lib.syncLoop(block.tx.length, function (subloop) {
-                var i = subloop.iteration();
-                Tx.findOne({txid: block.tx[i]}, function(err, tx) {
-                  if(tx) {
-                    tx = null;
-                    subloop.next();
-                  } else {
-                    save_tx(block.tx[i], function(err){
-                      if (err) {
-                        console.log(err);
-                      } else {
-                        console.log('%s: %s', block.height, block.tx[i]);
-                      }
-                      setTimeout( function(){
-                        tx = null;
-                        subloop.next();
-                      }, timeout);
+    is_locked(function (exists) {
+      if (exists) {
+        console.log("db_index lock file exists...");
+        return cb();
+      } else {
+        create_lock(function (){
+          var complete = false;
+          lib.syncLoop((end - start) + 1, function (loop) {
+            var x = loop.iteration();
+            if (x % 5000 === 0) {
+              Tx.find({}).where('blockindex').lt(start + x).sort({timestamp: 'desc'}).limit(settings.index.last_txs).exec(function(err, txs){
+                Stats.update({coin: coin}, {
+                  last: start + x - 1,
+                  last_txs: '' //not used anymore left to clear out existing objects
+                }, function() {});
+              });
+            }
+            lib.get_blockhash(start + x, function(blockhash){
+              if (blockhash) {
+                lib.get_block(blockhash, function(block) {
+                  if (block) {
+                    lib.syncLoop(block.tx.length, function (subloop) {
+                      var i = subloop.iteration();
+                      Tx.findOne({txid: block.tx[i]}, function(err, tx) {
+                        if(tx) {
+                          tx = null;
+                          subloop.next();
+                        } else {
+                          save_tx(block.tx[i], function(err){
+                            if (err) {
+                              console.log(err);
+                            } else {
+                              console.log('%s: %s', block.height, block.tx[i]);
+                            }
+                            setTimeout( function(){
+                              tx = null;
+                              subloop.next();
+                            }, timeout);
+                          });
+                        }
+                      });
+                    }, function(){
+                      blockhash = null;
+                      block = null;
+                      loop.next();
                     });
+                  } else {
+                    console.log('block not found: %s', blockhash);
+                    loop.next();
                   }
                 });
-              }, function(){
-                blockhash = null;
-                block = null;
+              } else {
                 loop.next();
+              }
+            });
+          }, function(){
+            Tx.find({}).sort({timestamp: 'desc'}).limit(settings.index.last_txs).exec(function(err, txs){
+              Stats.update({coin: coin}, {
+                last: end,
+                last_txs: '' //not used anymore left to clear out existing objects
+              }, function() {
+                remove_lock(function(){
+                  return cb();
+                });
               });
-            } else {
-              console.log('block not found: %s', blockhash);
-              loop.next();
-            }
+            });
           });
-        } else {
-          loop.next();
-        }
-      });
-    }, function(){
-      Tx.find({}).sort({timestamp: 'desc'}).limit(settings.index.last_txs).exec(function(err, txs){
-        Stats.update({coin: coin}, {
-          last: end,
-          last_txs: '' //not used anymore left to clear out existing objects
-        }, function() {
-          return cb();
         });
-      });
+      }
     });
   },
 
diff --git a/lib/settings.js b/lib/settings.js
index 668e7c7c1..ff3887dfb 100644
--- a/lib/settings.js
+++ b/lib/settings.js
@@ -126,6 +126,7 @@ exports.genesis_tx = "65f705d2f385dc85763a317b3ec000063003d6b039546af5d8195a5ec2
 exports.genesis_block = "b2926a56ca64e0cd2430347e383f63ad7092f406088b9b86d6d68c2a34baef51";
 
 exports.heavy = false;
+exports.lock_during_index = false;
 exports.txcount = 100;
 exports.show_sent_received = true;
 exports.supply = "COINBASE";
diff --git a/settings.json.template b/settings.json.template
index 0f898d68b..d252a869a 100644
--- a/settings.json.template
+++ b/settings.json.template
@@ -128,6 +128,9 @@
   //heavy (enable/disable additional heavy features)
   "heavy": false,
 
+  //disable saving blocks & TXs via API during indexing.
+  "lock_during_index": false,
+
   //amount of txs to index per address (stores latest n txs)
   "txcount": 100,