ParaGuard is the only fish and filter safe aldehyde based (10% by weight) parasite control product available. 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 on fish (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. For use in freshwater or marine.