Induced voltage may trip a solid state relay, but I'd doubt it would melt dry contacts...as you said, that's from too much current. Hwhy don't you just run the fountain with the lights off and try it, or is this unacceptable to the client?
Try contacting these guys with your problem, they sell controls as well, might have a solution or advice for you!
http://www.fountainpeople.com/site_2/index_home.htm Mike
