diff --git a/advanced-reactor.html b/advanced-reactor.html
index ff12949..73d66c2 100644
--- a/advanced-reactor.html
+++ b/advanced-reactor.html
@@ -19,7 +19,7 @@
             X_H_init: { value: 30., required: true },
             X_STO_init: { value: 0., required: true },
             X_A_init: { value: 0.001, required: true },
-            X_TS_init: { value: 125., required: true }
+            X_TS_init: { value: 125.0009, required: true }
         },
         inputs: 1,
         outputs: 1,
diff --git a/dependencies/reactor_class.js b/dependencies/reactor_class.js
index dcc5cfd..f1695e7 100644
--- a/dependencies/reactor_class.js
+++ b/dependencies/reactor_class.js
@@ -65,7 +65,7 @@ class Reactor_CSTR {
 
         const dC_total = math.multiply(math.add(dC_in, dC_out, r, t_O), time_step);
 
-        this.state = math.add(this.state, dC_total);
+        this.state = math.abs(math.add(this.state, dC_total)); // make sure that concentrations do not go negative
         return this.state;
     }
 }