Adding new fish with discus: quarantine + acclimation protocol

In short

• A 4-week quarantine is MANDATORY for ANY new species (including cheap tetras).
• A quarantine tank of at least 50L (13 US gal) with a cycled filter and a heater.
• Drip acclimation 1–2 hours — gradual equalization of TDS, pH, temperature.
• Preventive treatment in quarantine: Praziquantel + 0.1% salt (parasites + bacteria).
• Final integration: lights off 24h + rearrange the decor (reset territories).
• Major risks avoided: Hexamita (from angelfish), Camallanus (from guppy), Mycobacterium (anyone).

What you'll learn

Adding new fish to an already-established discus (Symphysodon) aquarium is one of the most dangerous operations — a single sick fish can wipe out the whole tank in 2–6 weeks. Hexamita, Camallanus, Mycobacterium, Ich and Columnaris are frequently transmitted through new fish bought without quarantine. This guide shows you the complete step-by-step protocol: quarantine, drip acclimation, preventive treatment, integration.

Why you can't add them directly

Risk 1: Hidden diseases at purchase

Stores and some breeders don't detect asymptomatic pathogens:

Risk 2: The stress of sudden acclimation

Differences between the store and your tank:

• TDS: could be 50 vs 200 ppm
• pH: 7.5 vs 6.5
• Temperature: 25°C (77°F) vs 29°C (84°F)
• Light, the presence of other fish, its own parameters

A sudden introduction = osmotic shock + acute stress = immunity collapses within 24h.

Risk 3: Disturbing the existing tank

Discus are semi-territorial. New fish in a settled tank = re-establishing hierarchies + temporary aggression.

The complete protocol — 6 stages

Stage 1: Preparing the quarantine tank (before purchase)

Minimal setup:

• A 50–80L (13–21 US gal) tank (empty or with simple plants)
• An internal or external filter with sponge + ceramic
• A 100W heater (29°C / 84°F if the species are tropical)
• A digital thermometer
• A lid if the species jump (hatchetfish, killifish)
• Simple plants (Anubias, Java moss) or no plants
• No substrate (visibility of feces + easy to clean)

A cycled filter: run the quarantine tank for 2–4 weeks before adding fish, with biological media from the main tank. Or use Seachem Stability.

Stage 2: Buying the fish

Questions to ask the source:

• ☐ What parameters does your water have? (pH, TDS, temp)
• ☐ What do you feed the fish?
• ☐ Are there any recent health problems in their tank?
• ☐ How long have you had the fish?
• ☐ Do you have quarantine / treatment records?

Red flags:

• ❌ "I don't know, just received from Asia"
• ❌ Fish with white feces, weight loss, nipped fins
• ❌ A store with visible mortality in the tanks
• ❌ Cloudy water in the store's tanks

Stage 3: Drip acclimation (1–2 hours)

Materials:

• A clean bucket
• A thin airline tube
• A valve/clamps to adjust the flow

Procedure:

1. Open the bag, empty the fish + their water into a clean bucket
2. Run the tube: one end in the quarantine tank, the other in the bucket
3. Start the siphon — water from the tank flows into the bucket
4. Adjust to 2–4 drops/sec (very slow)
5. Continue 60–120 minutes until the volume in the bucket doubles (or triples)
6. With a net, transfer the fish into the quarantine tank
7. DISCARD the water from the bucket — never into the tank

⚠️ Lights off in the quarantine tank for 24h after introduction.

Stage 4: A 4-week quarantine with observation

Week 1: Observation + stable parameters

• Light feeding (1×/day, a little food)
• Check daily: breathing, colors, behavior, feces
• Water test: ammonia (0), nitrites (0), nitrates (<20)
• No treatment yet — see how they adapt

Week 2: Preventive treatment (recommended)

For any new species (especially tetras, angelfish, livebearers):

• Praziquantel (PraziPro, Sera Tremazol): 1 dose per the product — anti internal and external parasites (Camallanus, Capillaria, Gyrodactylus)
• 0.1% salt (1 g/L): a mild antibacterial + reduces osmotic stress
• Garlic-soaked food (a natural antibacterial)

⚠️ Do NOT use copper if you plan to keep shrimp/snails.

Week 3: Back to normal

• Changes 30% × 2/week
• Feeding 2×/day
• Watch the feces: normal = OK, persistently white = Hexamita ⚠️

Week 4: Pre-integration

• The quarantine tank water = pH, TDS close to the main tank
• No signs of disease for 4 consecutive weeks
• The fish eat well, bright colors

Stage 5: Integration into the main tank

24h before:

• A 30% water change in the main tank
• Turn off the lights when you integrate
• Rearrange the decor (move the wood, plants) — reset the territories

The integration itself:

1. Catch the new fish with a clean net
2. Drip acclimation 30 minutes between quarantine and the main tank (parameters already close)
3. Release the fish on the opposite side of the tank from where the discus stay
4. Lights off 24h
5. Don't feed for 4–6 hours (all the fish are distracted by the change)

Stage 6: The first 7 days post-integration

Common mistakes

❌ "I don't quarantine — I buy from a trusted store" — Stores don't detect asymptomatic Hexamita. Quarantine is mandatory even for cheap tetras.

❌ "A 20L (5 US gal) quarantine tank for 5 cardinals" — Too small. Stress + unstable parameters = active disease, NOT prevention.

❌ "20-minute acclimation, let the bag float" — That only equalizes the temperature. For TDS and pH you need a 1–2 hour drip.

❌ "I'll add the bag water to the tank for acclimation" — You transfer exactly the pathogens you're trying to prevent. DISCARD the bag water.

❌ "Preventive Hexamita treatment for all fish" — Metronidazole without cause harms the microbiome. Use only Praziquantel + salt as a preventive. Metronidazole ONLY at clinical signs.

❌ "I'll add 1 fish alone to the existing cardinal group" — It will immediately be the target of attacks. Add at least 3–5 to strengthen the school.

Exceptions and special cases

Fish from a verified Discus.ro breeder

Quarantine reduced to 2 weeks (instead of 4) — verified breeders follow strict protocols. A full quarantine is still needed, only the duration can be shortened.

Species from the same breeder, from 2 different tanks

A separate quarantine for each source tank — don't mix them in quarantine. Different microbiomes = mutual stress.

Visibly sick fish at purchase

Do NOT buy. Return / don't pay / inform the breeder. The risk isn't worth any discount.

Complete introduction-protocol checklist

Before purchase:

• ☐ A 50L+ (13+ US gal) quarantine tank, cycled
• ☐ Praziquantel + salt available
• ☐ A 4-week plan reserved

At purchase:

• ☐ Questions for the source (parameters, food, health)
• ☐ Inspect the fish (colors, behavior, feces if visible)
• ☐ A fast transport plan (max 2h)

Acclimation:

• ☐ Drip 1–2 hours
• ☐ Discard the bag water
• ☐ Lights off 24h

Quarantine:

• ☐ Week 1: observation
• ☐ Week 2: Prazi + salt
• ☐ Week 3: back to normal
• ☐ Week 4: pre-integration

Integration:

• ☐ Rearrange the main tank
• ☐ Lights off 24h
• ☐ 7-day monitoring

What to do next

📚 Learn more:

• Quarantine protocol (4 weeks) — advanced details
• Best discus tank mates
• Fish to avoid with discus
• Hexamita and HITH
• Internal worms (Camallanus)
• Essential aquarist pharmacy

🧮 Calculate:

• Quarantine tank volume calculator
• Water change calculator

🛒 Buy:

• Praziquantel + aquarium salt
• An internal filter for the quarantine tank