django template zibs

"""
Error
Django Version: 1.6
Exception Type: TypeError
Exception Value:
cannot concatenate 'str' and 'QuerySet' objects
"""
#models.py
class Service(models.Model):
    service_name = models.CharField(max_length="250")
    service_port = models.IntegerField(max_length="200")
    box = models.ForeignKey(Box)

    class Meta:
        verbose_name_plural="services"

    def __unicode__(self):
        return self.service_name

#views.py

def get_box_services(request):
    box_id = request.GET.get("box_id", "")
    box_services = Service.objects.filter(box_id=box_id)
    render_to_response("box_services.html",
                       {"box_services":box_services})


#template
<table border="0" cellspacing="5" cellpadding="5">
            <tr>
                <th>Service Name</th><th>Port</th><th>Options</th>
            </tr>
            {% for box_service in box_services %}
            <tr>
                <td>{{box_service.service_name}}</td>
                <td>{{box_service.service_port}}</td>
                <td>Start|Stop|Restart</td>
            </tr>
            {% endfor %}
        </table>