Quick answer: Keep a few core medications on hand so you can act fast: a broad antiparasitic like Seachem ParaGuard, a bacterial treatment like Fritz Maracyn or Seachem Kanaplex, and an ich treatment like Ich-X. Diagnose the problem before you dose, because the wrong medication wastes time and can kill your beneficial bacteria. Test and stabilize your water first, since many illnesses come from poor conditions rather than an actual pathogen.
Before you medicate gasping or struggling fish
If fish are gasping, breathing fast, clamping fins, or acting sick right after a cleaning, water change, heat spike, or overfeeding, do not make medication the first move. Check oxygen, ammonia, nitrite, temperature, and recent tank changes first, because poisoned or low-oxygen water can look like disease.
Fish medication treats parasites, fungus, and bacterial infections; it does not fix low oxygen, ammonia poisoning, nitrite stress, chlorine exposure, or a damaged biofilter. DBC Aquatics uses medication only after the rescue basics are safe enough for the fish to handle treatment.
- If fish are gasping at the top, use the fish gasping rescue guide before choosing medicine.
- If ammonia or nitrite is above zero, follow the ammonia spike emergency guide first.
- If you are not sure whether this is disease or water stress, start with the DBC Aquatics Symptoms Checker.
Top 5 Fish Medications and When to Use Them
Don’t wait until your fish are gasping for life to take action — these are the top meds every aquarist should keep in their arsenal, and exactly when to use them.
When something seems off in your aquarium — like flashing, white spots, or bloating — the wrong medication can do more harm than good. This post covers the five most effective over-the-counter fish treatments, with real-world guidance on symptoms, dosing, and quarantine tips.
Why You Shouldn’t Medicate Blindly
Before using any medication, it’s essential to diagnose the problem. Treating the wrong condition can stress fish, destroy your beneficial bacteria, and waste time.
Use this guide with our Diagnose Sick Fish Symptoms Guide and Fish Health Checklist to pinpoint the issue before medicating.
1. Seachem ParaGuard
- Best for: External parasites, fungus, mild bacterial infections
- Symptoms: Ich, velvet, flukes, mouth fungus, early fin rot
- Dosage: 5 mL per 10 gallons daily for up to 14 days
ParaGuard is a gentler alternative to copper or formalin, making it safe for most freshwater fish and tanks with sensitive plants.
- Remove carbon and UV filters before use
- Not effective for internal parasites
- Best used in a separate hospital tank
🔗 Related: Quarantine Tank Setup Guide
2. API General Cure (or Fin & Body + Expel-P)
- Best for: Internal parasites, protozoans
- Symptoms: Stringy poop, weight loss, scratching, bloating
- Dosage: 1 packet per 10 gallons; repeat every 48 hours (3x)
This combo targets both protozoan infections and internal worms. Use in quarantine tanks and consider medicated food for internal dosing.
- Combine with Seachem Focus for food binding
- Do not overdose
- Great for guppies, bettas, and community tanks
🔗 Related: Feeding Sick Fish Tips
3. Fritz Maracyn
- Best for: Bacterial infections (gram-positive)
- Symptoms: Fin rot, cotton mouth, popeye, ulcers
- Dosage: 1 packet per 10 gallons daily for 5 days
Maracyn is erythromycin-based and effective against early-stage bacterial infections, especially when caught quickly.
- Safe for in-tank use
- Replace carbon after treatment
- Combine with Maracyn 2 for broader protection
🔗 Related: Fin Rot Symptoms & Fixes
4. Ich-X by Hikari
- Best for: Ich, velvet, mild fungal infections
- Symptoms: White spots, dusty gold coating, surface rubbing
- Dosage: 5 mL per 10 gallons initially; partial redose daily
Ich-X combines malachite green and formalin for maximum impact against protozoa. Use carefully — it’s not shrimp-safe.
- Remove carbon and increase aeration
- Treat for 3–5 days after symptoms vanish
- Not for use with scaleless fish or inverts
🔗 Related: Ich Prevention Best Practices
5. Seachem Kanaplex
- Best for: Internal bacterial infections, dropsy, popeye
- Symptoms: Pineconing, cloudy eyes, bloating, lethargy
- Dosage: 1 scoop per 5 gallons every 2 days (3x)
Kanaplex treats systemic bacterial issues and is one of the few meds that works when absorbed via food or gills. Use with Focus to bind to food.
- Combine with Metroplex for deep infections
- Watch ammonia levels
- Use in quarantine if fish is visibly bloated
🔗 Related: Dropsy Diagnosis & Management
Medication Safety and Quarantine Tips
- Always quarantine sick or new fish to avoid contaminating the main tank
- Remove carbon and UV sterilizers during treatment
- Use an air stone to boost oxygen during medication
- Monitor water quality, especially ammonia and nitrites
When in doubt, test your water first. Many illnesses stem from poor conditions, not disease.
Medication Cabinet Checklist
| Medication | Use For |
|---|---|
| ParaGuard | External parasites, fungus |
| General Cure | Internal parasites |
| Maracyn | Bacterial infections |
| Ich-X | Ich, velvet, fungus |
| Kanaplex | Internal bacterial issues |
Final Thoughts
The key to saving your fish isn’t in your medication drawer — it’s in early detection and accurate diagnosis. Treat the illness, not just the symptoms.
- Don’t medicate without identifying the problem
- Use a quarantine tank whenever possible
- Always test water before and during treatment
🔗 Start here: Diagnose Sick Fish Symptoms Guide
📄 Download this as a printable Fish Health Checklist
What’s Next?
🎥 Subscribe to DBC Aquatics on YouTube for weekly fish care tips, product reviews, and Q&As with real-world aquarists.
Before you medicate
Run the rescue checklist before dosing medicine
Most sick-looking fish need water, oxygen, and temperature checked before medication. Email yourself the checklist so you do not treat ammonia, nitrite, or stress like a disease.
Run the rescue checklist before dosing medicine
Most sick-looking fish need water, oxygen, and temperature checked before medication. Email yourself the checklist so you do not treat ammonia, nitrite, or stress like a disease.
Rescue kit
Keep the emergency basics ready
If you are buying medication, build the basics first: water test kit, dechlorinator, air pump, thermometer, and a clean hospital container. I put those together in the Aquarium Rescue Kit so medication stays the second step, not the first panic move. See the Aquarium Rescue Kit.
Frequently asked questions
What fish medications should every fishkeeper keep on hand?
A small core kit covers most situations: Seachem ParaGuard for external parasites, fungus, and mild bacterial issues; API General Cure for internal parasites and protozoans; Fritz Maracyn for gram-positive bacterial infections; Ich-X for ich and velvet; and Seachem Kanaplex for internal bacterial infections like dropsy and popeye. Having these ready means you are not scrambling to a store while a fish gets worse. This is educational guidance, not veterinary advice, so confirm the diagnosis before reaching for any of them.
Do I need to remove carbon before dosing medication?
Yes. Activated carbon and similar chemical media pull medication right out of the water, so the dose never reaches a therapeutic level. Pull the carbon and shut off any UV sterilizer before you treat. With several meds, such as Maracyn, you replace the carbon only after the treatment course is finished.
Can I treat in the main tank or should I use a hospital tank?
A separate hospital or quarantine tank is the safer choice for most treatments, including ParaGuard, General Cure, and Kanaplex. It keeps medication off your plants, inverts, and biofilter, and lets you dose precisely. Some products like Maracyn are labeled safe for in-tank use, but isolating a sick fish also stops disease from spreading to the rest of the tank.
Will these medications harm shrimp, snails, or plants?
Some will. Ich-X combines malachite green and formalin and is not shrimp-safe, and it should not be used with scaleless fish or other inverts. ParaGuard is gentler and friendlier to sensitive plants, but a hospital tank is still the cleanest way to avoid risking your invertebrates. Always read the label for invert and plant warnings before dosing a tank that holds them.
How do I know what disease I’m actually treating?
Match the symptoms to the condition before you dose. White spots and surface rubbing point to ich; stringy poop, weight loss, and bloating suggest internal parasites; fin rot, cotton mouth, and popeye indicate bacterial infection; and pineconing or dropsy points to a systemic internal bacterial issue. Pair your observations with a symptom guide and a health checklist, and remember this is educational, not a substitute for diagnosing the specific case in front of you.
Why isn’t the medication working?
The most common reason is treating the wrong illness, so a bacterial med does nothing against a parasite and vice versa. Other causes are leaving carbon or a UV sterilizer running, which strips the dose, underdosing, or stopping too early before the full course is done. Poor water quality also undermines treatment, so test ammonia and nitrites and fix the conditions, because many illnesses stem from water problems rather than disease.
Author and editorial note
Written and maintained by Benjamin Thoden, founder of DBC Aquatics. This shrimp guide is reviewed through DBC Aquatics’ stability-first lens: cycle maturity, mineral consistency, molt safety, copper risk, grazing surfaces, and slow acclimation matter more than quick fixes. See our editorial standards for how guides are created, reviewed, and updated.
Fish medication decision table: treat the cause, not the panic
Medication is most useful after water quality and oxygen are safe. Many disease-like symptoms come from ammonia, nitrite, chlorine, low oxygen, temperature shock, bullying, or a dirty filter. If those are still active, medication can add stress without solving the cause.
| Main signs | Rule out first | Medication direction to research | Do not do |
|---|---|---|---|
| White salt-like spots, scratching, rapid spread | Temperature swings and water stress | Ich medication such as Ich-X style treatments, following label directions | Stop treatment as soon as spots vanish; the parasite cycle may still continue. |
| Stringy waste, weight loss, worms, internal parasite signs | Starvation, bullying, poor diet | Internal parasite medication such as praziquantel/metronidazole-based options where legal | Treat the display tank blindly if only one fish is affected and quarantine is possible. |
| Fin rot, ulcers, cloudy patches, bacterial signs | Ammonia/nitrite burn and aggression | Antibacterial medication matched to symptoms and local availability | Mix antibiotics casually or dose without aeration and water monitoring. |
| External slime, flashing, mild parasite/fungal concern | Water irritants, chlorine, pH shock | Broad external treatment only when symptoms fit | Use ?just in case? medication after every new fish instead of quarantine observation. |
| Unknown sickness | All water/environment causes | Quarantine, observation, photos, expert help | Throw multiple medications into the tank at once. |
Before dosing checklist
Test ammonia and nitrite, check temperature, increase aeration, remove carbon if the medication label requires it, confirm the tank volume, and read whether the medication is safe for shrimp, snails, scaleless fish, plants, and biological filtration. Write down the first dose time so you do not accidentally double-dose.
When to get help
If fish keep dying despite safe water and careful treatment, bring clear photos, water results, stocking, tank size, and a timeline to a qualified aquatic veterinarian, experienced local fish store, breeder, or specialist. Guessing is expensive; a good timeline often reveals the actual cause.
Before you medicate a struggling tank
If fish are gasping, hiding, clamped, or acting strange after a water change, start at the Aquarium Rescue Hub first. Medication helps the right problem, but ammonia, nitrite, chlorine, low oxygen, and temperature shock need water fixes before medicine.
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