Hikari Ich-X is one of the most widely used over-the-counter aquarium treatments for ich (white spot disease) and velvet in freshwater fish. It combines formalin (a formaldehyde solution) with malachite green — two old but still effective antiparasitic and antifungal compounds. Ich-X is an over-the-counter aquarium product, not a prescription-grade veterinary medication, and is intended for use in hobby aquariums. For valuable koi, show fish, or complex marine and reef systems, consultation with an aquatic veterinarian is strongly recommended before treatment.

Overview

Formalin disrupts parasite cell membranes and is broadly effective against ich trophonts in their free-swimming stage, external protozoans, and some fungi. Malachite green is a triphenylmethane dye that acts as both an antiparasitic and antifungal agent, also effective against Saprolegnia on fish and eggs. Together, these ingredients provide broader coverage than either alone and form the backbone of many hobbyist ich treatments.

Ich-X is formulated for freshwater aquariums but is sometimes used at reduced doses in certain marine situations. It is not reef-safe — it will harm invertebrates, corals, and live plants at full dose.

Uses

  • Ich (Ichthyophthirius multifiliis) in freshwater fish
  • Freshwater velvet (Piscinoodinium)
  • Saprolegnia and other fungal infections on fish and eggs
  • External protozoan infections
  • Preventive use on eggs to reduce fungal growth in breeding setups

Dosage

Ich-X is dosed per gallon of tank water. Typical label dosing:

  • Standard dose: 5 mL per 10 gallons daily for at least 3 days after the last visible spot disappears (often 10 to 14 days total)
  • Scaleless fish dose: Half the standard dose — tetras, loaches, catfish, elephant nose, and other scaleless species
  • Continue daily dosing throughout the parasite lifecycle
  • Water changes of 25% between doses are optional but can improve water quality during long treatment courses

Always follow the product label, which is the definitive dosing reference. Consult an aquatic veterinarian for valuable fish or unusual situations.

Safety Considerations

  • Scaleless fish — Loaches, catfish, tetras, eels, and similar species are more sensitive. Use half dose.
  • Invertebrates — Shrimp, snails, and corals are highly sensitive to formalin and malachite green. Do not use in invertebrate tanks or reef systems.
  • Live plants — Malachite green can stain plants and may harm sensitive species. Many hobbyists report plants tolerate reduced doses, but damage is possible.
  • Fry and eggs — Can be used at reduced dose on eggs but may be harsh on newly hatched fry. Read species-specific guidance.
  • User safety — Formalin is a carcinogen. Avoid skin contact, wear gloves, and do not inhale vapors.
  • Oxygenation — Reduces dissolved oxygen slightly. Ensure surface agitation and additional aeration during treatment.

Water Chemistry Effects

  • Slight reduction in dissolved oxygen
  • No significant effect on pH or hardness at therapeutic doses
  • Malachite green stains silicone, plastic decor, and sealant blue-green. This is cosmetic but often permanent.
  • Treatment residues are removed with water changes and activated carbon after treatment is complete

How to Use

  1. Test water parameters and perform a water change if ammonia or nitrite are elevated
  2. Remove activated carbon from the filter; leave biological filtration in place
  3. Shake the bottle well before use
  4. Add the correct dose based on total tank volume (remember decor displaces water)
  5. Use half dose if scaleless fish or sensitive species are present
  6. Dose daily for at least 3 days after the last visible spot disappears
  7. Maintain excellent oxygenation throughout treatment
  8. After treatment, perform a 25 to 50% water change and return activated carbon to the filter

FAQs

Is Ich-X reef safe? No. It is not safe for invertebrates, corals, or live rock communities.

Can I use Ich-X with salt? Light salt dosing is compatible with Ich-X in salt-tolerant freshwater species.

Will it kill my plants? Most hardy aquarium plants tolerate reduced doses, but sensitive species may be damaged. Anubias, java fern, and moss are generally tolerant.

How long does treatment take? Typically 10 to 14 days to cover the full ich lifecycle. Do not stop early, even if spots disappear.

Can I use Ich-X with other medications? Avoid combining with other harsh medications. Always seek veterinary advice before layering treatments.