Removes ectoparasites and fungal, bacterial and viral lesions. Safe dosing. Will not adversely affect the bio-filter. ParaGuard is the only aldehyde-based pest control product that is safe for fish and the filter (for fish parasites). Unlike highly toxic and difficult to use formalin-based drugs, ParaGuard contains no formaldehyde or methanol and does not alter pH. ParaGuard uses a proprietary synergistic blend of aldehydes, malachite green and fish-protecting polymers that effectively eradicate many ectoparasites. It also treats external fungal/bacterial/viral lesions (e.g. fin rot). It is particularly useful in quarantine. 100 ml treats 800 l.