ParaGuard is the only fish and filter-safe aldehyde-based (10% by weight) parasite control product available (for parasites on fish). Unlike highly toxic and difficult-to-use formalin-based medications, ParaGuard contains no formaldehyde or methanol and will not alter pH. ParaGuard? employs a proprietary synergistic blend of aldehydes, malachite green, and fish protective polymers that effectively and efficiently eradicates many ectoparasites (e.g., ich, etc.) and external fungal/bacterial/viral lesions (e.g. fin rot). It is particularly useful in hospital and receiving tanks for new fish and whenever new fish are introduced to a community tank.