Don't expect overnight results, it could take 6 weeks.
I think their diet makes a big difference. A few weeks ago we went up to Ventura County to fix the house after the last renters. The lads went along and I forgot their food. We got them some Iams that afternoon. All seemed ok. Next AM dh drove off to work with it so I got them some Beniful. They ate it. No problems, or so I thought. I only had a small travel bowl for them so I didn't think so much about refilling it so often. After we got home I found that they are drinking about 3 times as much as before. I'm picking up a new bag of Wellness tomorrow.
I wonder what would happen if I fed them Old Roy. (shudder)(td)