How do I stop a pvc leak?

I recently made a PVC connection into my swimming pool plumbing to add a fountain. At the one joint I made where a 90 degree elbow meets a ball valve I noticed a small leak (about 1 drop every 15-20 seconds) . Unfortunately the way I made the connection I cannot cut it out and replace it because I did the elbow and ball valve to close together. You can see a picture of this at: http://grovevillefire.com/ron/pvc.jpg Is there anything I can do or is there anything that is sold that can stop the leak?