ParaGuard, 20 L / 5.3 fl. gal. Fish and filter safe parasite control The only fish and filter safe aldehyde based parasite control product available (for parasites on fish) Employs a proprietary, synergistic blend of aldehydes, malachite green, and fish protective polymers Effectively and efficiently eradicates many ectoparasites (ich, etc) and external fungal, bacterial, and viral lesions (fin rot) 250 milliliters treats 500 US gallons