White Spot Disease (Ich) in Aquariums – Vet Guide 2025 🐠🧬

If your fish look like they've been sprinkled with salt, you may be facing a common but serious parasite—White Spot Disease, or "Ich." 🧂 I’m Dr Duncan Houston BVSc, and this guide covers the science, symptoms, and best treatment options to combat Ich in both freshwater and marine aquariums 🧪

🔬 What Is White Spot Disease (Ich)?

Ich is a protozoal infection marked by visible white cysts on the skin and gills. Though freshwater and saltwater Ich are caused by different organisms, the signs and treatment logic are similar:

• Freshwater Ich: Ichthyophthirius multifiliis
• Marine Ich: Cryptocaryon irritans

🧫 Diagnosis

To confirm Ich:

• Scrape gills or skin near cysts
• Mix sample with tank water on a slide
• View under 100x–400x microscope

Freshwater “Ich” Identification

• Large, dark, ciliated “trophonts” with a horseshoe-shaped nucleus 🧲
• Smaller “tomites” move rapidly and are translucent

Marine “Ich” Identification

• Spherical/pear-shaped ciliated protozoans 🧬
• Distinct “rolling” movement under the scope

📈 Transmission & Lifecycle

• Spread is fast in high-density tanks 🏘️
• Can come in on new fish, plants, or contaminated water
• Warmer water = faster parasite replication 🌡️
• Free-swimming “theronts” infect fish and encyst as “trophonts”

🧍‍♂️ Symptoms of Ich

• Visible white cysts (~1 mm)
• “Flashing” – rubbing on rocks/decor
• Frayed fins, ulcers, excessive mucus 🩸
• Respiratory distress – flared gills, gulping
• Secondary infections often follow if untreated

🚨 Why Act Quickly?

Ich can cause organ failure, immune suppression, and death if left untreated. Its lifecycle allows it to persist invisibly before exploding into a tank-wide crisis ⚠️

🛡️ Treatment & Prevention Strategies

🧼 1. Quarantine Protocol

• Quarantine all new fish for 3–6 weeks at 24–27°C
• Tomonts release theronts, which die if no host is present in 24–48 hours
• Marine tanks: remove all fish & leave tank fallow, maintain stable temp

💧 2. Osmotic Adjustment

Marine (Hyposalinity):

• Lower salinity to 1.015 over several days (1.005 per day)
• Maintain for 21–30 days in quarantine tank

Freshwater (Hypersalinity):

• Add 15 g pure salt per 3.8 L water
• Reach SG ~1.002–1.003
• Treat for 7 days, then slowly remove salt via water changes

🔬 3. Copper Treatment

• Only in fish-only tanks (TOXIC to inverts!) ☠️
• Free Cu²⁺: 0.15–0.20 mg/L maintained for 3–6 weeks
• Introduce slowly over 2–3 days
• Monitor daily with copper test kit

🧪 4. Formalin Baths

• Use only in well-aerated tanks (formalin reduces O₂!)
• Bath: 0.15–0.25 mL/L for 1 hour daily, up to 3 days
• Prolonged: 0.015–0.025 mL/L every 3–4 days with water changes
• Don’t use with gill disease or in invertebrate tanks

🌿 5. Malachite Green

• Quarantine tanks only—avoid with inverts
• Bath: 1–2 mg/L for 30–60 mins, max 4 days
• Prolonged: 0.1–0.25 mg/L every 3 days (3 doses)
• Follow with partial water changes

🧬 6. Chloroquine

• Broad-spectrum protozoa control
• Use at 10 mg/L in quarantine tank for 2–3 weeks
• Pair with hyposalinity/hypersalinity and warm temps

🔆 7. UV Sterilisation

• Effective only against free-swimming theronts
• Not helpful against encysted stages or in reef tanks 🌊
• May reduce severity but not a stand-alone cure

📌 Post-Treatment Tips

• Re-dose beneficial bacteria post-formalin/malachite/copper use 🧫
• Do not use treatments in reef tanks unless confirmed safe for inverts
• Resume UV steriliser and lighting after treatment if previously disabled
• Disinfect nets, buckets, and hands between tanks 🔁

👨‍⚕️ When to Contact a Vet

• Rapid breathing or gill damage
• Unidentified secondary infections
• Recurring Ich despite treatment
• Need help choosing a safe quarantine protocol

Use the Ask A Vet app for personalised treatment plans and medication safety checks 📲🧑‍⚕️

🧠 Summary: Beat Ich in 2025

• ✔️ Confirm Ich with microscope
• ✔️ Isolate infected fish ASAP
• ✔️ Use temperature & salinity to your advantage
• ✔️ Choose treatments based on tank type (reef vs fish-only)
• ✔️ Clean equipment and re-establish bio-filtration after meds

White Spot Disease can be aggressive, but with swift action and the right knowledge, your tank can recover and thrive 🐠💪. Stay informed, treat responsibly—and if in doubt, Ask A Vet is here to help!

— Dr Duncan Houston BVSc