Change speed on Touch

So this code scrolls background infinitely. I have a problem in the Touch part. The scrollSpeed slows down each time when i tap. I want it to slow down the scrollSpeed on tap and when it slowed, go to initial scrollSpeed on a next tap. There is the problem inside the for loop. Please help. Thanks in advance!

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class BackgroundScroller : MonoBehaviour {

 [SerializeField]
 private float scrollSpeed;

 [SerializeField]
 private float tileSizeZ;

 private Vector2 saveOffset;
 private Vector3 startPosition;

 private bool isSlowed = false;


 // Use this for initialization
 void Start ()
 {
     startPosition = transform.position;
     saveOffset = GetComponent<Renderer>().sharedMaterial.GetTextureOffset("_MainTex");
 }
 
 // Update is called once per frame
 void FixedUpdate ()
 {

     float x = Mathf.Repeat(Time.time * scrollSpeed, tileSizeZ * 4);
     x = x / tileSizeZ;
     x = Mathf.Floor(x);
     x = x / 4;

     Vector2 offset = new Vector2(saveOffset.x, saveOffset.y);
     GetComponent<Renderer>().sharedMaterial.SetTextureOffset("_MainTex", offset);

     float newPosition = Mathf.Repeat(Time.time * scrollSpeed, tileSizeZ);
     transform.position = startPosition + Vector3.up * newPosition;

     //Touch part
     for (int i = 0; i < Input.touchCount; i++)
     {
         if (Input.GetTouch(i).phase == TouchPhase.Began && isSlowed == false)
         {
             scrollSpeed = scrollSpeed / 2;
             isSlowed = true;
         }
         else if (Input.GetTouch(i).phase == TouchPhase.Began && isSlowed == true)
         {
             scrollSpeed = scrollSpeed;
             isSlowed = false;
         }
     }
 }

 void OnDisable()
 {
     GetComponent<Renderer>().sharedMaterial.SetTextureOffset("_MainTex", saveOffset);
 }

}