diff --git a/dependencies/asm3_class.js b/dependencies/asm3_class.js
index 1cf4ec0..93c7364 100644
--- a/dependencies/asm3_class.js
+++ b/dependencies/asm3_class.js
@@ -61,9 +61,8 @@ class ASM3 {
     i_cNO:   -1/14  // charge per S_NO                [mole H+ g-1 NO3-N]
   }
 
-  constructor(state) {
+  constructor() {
     // S_O, S_I, S_S, S_NH, S_N2, S_NO, S_HCO, X_I, X_S, X_H, X_STO, X_A, X_TS
-    this.state = state;
     this.stoi_matrix = this._initialise_stoi_matrix()
   }
 
@@ -96,10 +95,10 @@ class ASM3 {
     return K / (K + c);
   }
 
-  compute_rates(state) { // computes reaction rates. state is optional, if not provided, use class state
+  compute_rates(state) { // computes reaction rates. state is optional
 
     const rates = Array(12);
-    const [S_O, S_I, S_S, S_NH, S_N2, S_NO, S_HCO, X_I, X_S, X_H, X_STO, X_A, X_TS] = state || this.state;
+    const [S_O, S_I, S_S, S_NH, S_N2, S_NO, S_HCO, X_I, X_S, X_H, X_STO, X_A, X_TS] = state;
     const { k_H, K_X, k_STO, nu_NO, K_O, K_NO, K_S, K_STO, mu_H_max, K_NH, K_HCO, b_H_O, b_H_NO, b_STO_O, b_STO_NO, mu_A_max, K_A_NH, K_A_O, K_A_HCO, b_A_O, b_A_NO } = this.kin_params;
     
     // Hydrolysis
@@ -123,12 +122,9 @@ class ASM3 {
     return rates;
   }
 
-  compute_dC(dt){ // compute change in concentration over time step dt
-    return math.multiply(math.multiply(this.stoi_matrix, this.compute_rates()), dt);
+  compute_dC(state){ // compute changes in concentrations
+    return math.multiply(this.stoi_matrix, this.compute_rates(state));
   }
 }
 
-// testing stuff
-const asm3 = new ASM3([0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1])
-console.log(asm3.compute_rates())
-console.log(asm3.compute_dC(0.001))
\ No newline at end of file
+module.exports = ASM3;
\ No newline at end of file
diff --git a/dependencies/reactor_class.js b/dependencies/reactor_class.js
new file mode 100644
index 0000000..04527e8
--- /dev/null
+++ b/dependencies/reactor_class.js
@@ -0,0 +1,21 @@
+const ASM3 = require('./asm3_class')
+const math = require('mathjs')
+
+class Reactor_CSTR {
+    
+    constructor(initial_state){
+        this.state = initial_state;
+        this.asm = new ASM3();
+    }
+
+    tick_fe(time_step){ // tick reactor state using forward Euler method
+        const delta = this.asm.compute_dC(this.state);
+        this.state = math.add(this.state, math.multiply(delta, time_step));
+        return this.state;
+    }
+}
+
+// testing stuff
+let state = [0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1];
+const Reactor = new Reactor_CSTR(state);
+console.log(Reactor.tick_fe(0.001));
\ No newline at end of file