1. Use deionized water for water bath.
2. Add an algicide into the water bath to keep algae from growing.
Copper sulfate and copper containing algicides have been frequently used.
Excess copper, however, may be hazardous to the local environment.
There are several non-copper algicides:
Bath Clear Algicide
Clear Bath Algae Inhibitor
Add 10-15 drops per gallon of water.