Band-pass filters for guiding or controlling crystal polymorphism in water are provided. Band-pass filters convert a passive energy source to a spectral energy pattern tuned to resonant with different types of molecular oscillations pertinent to water. Tuned energy patterns convert problematic insoluble crystals to more thermodynamically stable and soluble crystals. Methods include use of the band-pass filter in water and design of band-pass filter parameters for optimal use on a particular water source.