How to convert Collision to Collider

I’m programming buoyancy from unite 2015, and I have a problem. I’ve done it all well, except for the fact that it only works with non-trigger colliders. How would I fix that?

using UnityEngine;
using System.Collections;

public class Buoyancy : MonoBehaviour {

    private Rigidbody subjectRigidbody;
    private BoxCollider box;

	// Use this for initialization
	void Start () {
        box = GetComponent<BoxCollider>();
        subjectRigidbody = GetComponent<Rigidbody>();
	}
	
	// Update is called once per frame
	void Update () {
        
	}

    void OnCollisionStay(Collision collision)
    {
        foreach (ContactPoint contact in collision.contacts)
        {
            subjectRigidbody.AddForce(Vector3.up * 20);
            subjectRigidbody.AddForce(subjectRigidbody.velocity * -1);
        }
    }
}

use other.collider