Note: You must add preservative into the globe.The preservative is availiable from the 
company selling Fimo Clay, it is a 10ml bottle with brush, just put one or two drops into 
the globe and the water will be clear for over a year, as I had tested it.
I also understand that those people maintaining the swimming pools, have some kind of 
preservative to keep the pool water crystal clear, maybe you can contact them.