First Steps After Buying Aquarium Fish: Beginner’s Guide for New Fish Owners
Welcome to your first day as a fish keeper! This quick-start guide walks you through what to do in the first hour, first day, and first week after you bring your new fish home. It’s written for beginners, with notes for both tropical freshwater and marine keepers. If you need help, pop into Birchwood Aquatic Centre or call 01322 664397.
Quick-Start Checklist (First Hour)
- Turn off aquarium lights to reduce stress.
- Float the closed bag for 15–20 minutes to equalise temperature.
- Prepare dechlorinated water (and matched salinity/ temperature for marine).
- Plan your acclimation: drip (best) or float-and-add-small-amounts.
- Dim the room, keep noise low, and keep curious pets/ kids back.
New to testing and the nitrogen cycle? See our How to Cycle Your Aquarium
Step-by-Step: Safe Acclimation
Option A — Drip Acclimation (safest for sensitive fish/ inverts)
- Float the sealed bag for 15–20 minutes.
- Open the bag, roll the top to make it float in a clean bucket or box.
- Start a siphon drip from your tank (use airline tube + valve/ knot) at ~2–4 drops/sec.
- When the volume doubles, discard half and continue dripping to double again (30–60 min total; up to 60 mins max for marine/ inverts).
- Net the fish into the tank. Discard acclimation water.
Option B — Float & Small Additions (hardier freshwater fish)
- Float 15–20 minutes.
- Open bag; add a small cup of tank water every minute for 5 minutes.
- Net the fish into the tank. Discard bag water.
Feed very lightly (or not at all) on the first evening.
First Day to First Week Plan
Day 0 (evening):
- Observe breathing, posture, and swimming.
- Offer a tiny feed only if fish are settled (skip if stressed). Remove uneaten food after 2–3 minutes.
- Keep lights dim/short.
Days 1–3:
- Test ammonia & nitrite daily.
- Small, frequent feeds (1–2×/day, tiny amounts).
- For marine tanks, verify salinity is stable.
- If ammonia or nitrite appears, do a 10–25% water change with matched-temp, dechlorinated (and for marine, salinity-matched) water.
Days 4–7:
- Continue testing.
- If all readings are safe, you may very gradually lengthen the photoperiod and feeding.
- Do not add more fish yet. Let your filter bacteria catch up first.
Quarantine (Highly Recommended)
If you have other fish, use a simple, bare quarantine tank (heater, filter, hiding place) for 2–4 weeks. It protects your display tank from parasites and allows targeted treatment if needed.
Feeding Basics
- Start with what your species naturally eats (flake, micro-pellet, frozen, algae wafers, live foods).
- Less is more: only what’s eaten in 2–3 minutes.
- Offer variety across the week for balanced nutrition.
- For marine, rinse frozen foods to reduce phosphate.
Water & Salt Notes
- Dechlorinate all tap water before it touches fish or filter media.
- For RO users and marine keepers, see RO Water & Salt Mixes.
- Match temperature (and salinity for marine) before water changes.
Common First-Week Mistakes (and Fixes)
- Adding too many fish too soon → add stock slowly; test and wait for stable zero ammonia/nitrite.
- Overfeeding → tiny portions; siphon leftovers; consider feeding tongs for shy fish.
- Skipping dechlorinator → always treat replacement water.
- Washing media under the tap → gently swish in old tank water to save bacteria.
- Lights on too long → 6–8 hours; increase gradually to curb algae.
- Mixing incompatible species → confirm with our Compatibility Guide.
When to Contact Us Urgently
- Fish gasping at surface, clamped fins, rapid breathing.
- Visible white spots, frayed fins, cottony growths.
- Ammonia >0.2 mg/L or any nitrite reading.
Call 01322 664397 or visit us—bring a water sample for testing.