Essential Guide to Freshwater Aquarium Fish Care in 2025 🐠

Welcome! I’m Dr Duncan Houston BVSc, and I’m thrilled to walk you through setting up and caring for your first freshwater aquarium. Whether you're hobby-curious or ready to take the plunge, this guide delivers expert insights, easy tips, and medical‑grade clarity to help you become a confident aquarist in 2025.

📏 1. Choosing the Right Tank Size

Your aquarium is a micro-ecosystem. Bigger tanks provide more stable water chemistry and forgiving conditions—ideal for beginners.

• Small tanks (≤20 L): Compact, stylish—but require vigilance due to rapid water parameter fluctuations.
• Medium tanks (40–100 L): Great balance for beginners—easier to manage, more stocking flexibility.
• Large tanks (100 L+): Highly stable, plenty of room—but cost more and require stronger equipment.

🐟 2. Selecting Fish Types

Fish come in all shapes, sizes, and temperaments. Consider:

• Adult size: Goldfish and cichlids get big—ensure you have room.
• Origin: African cichlids prefer alkaline, hard water. Amazon tetras thrive in soft, slightly acidic setups.
• Temperament: Mix species with compatible personalities to avoid bullying or stress.
• Ask us! Need help? Reach out to Ask A Vet via our app—we're here to guide your selections.

💧 3. Filtration—Your Biological Backbone

Filtration removes waste, maintains water clarity, and supports beneficial bacteria essential for fish health:

Filtration Stages

• Mechanical: Sponges or wool capture debris—clean weekly or monthly.
• Chemical: Activated carbon or resins absorb organics, odors, and discoloration.
• Biological: Media like bio-balls or ceramic rings house nitrifying bacteria to detoxify ammonia → nitrite → nitrate.

Filter Types & Best Uses

1. Sponge filters: Gentle, ideal for breeding, shrimp, or hospital tanks.
2. Internal filters: Good for nano setups, but cleaning can disturb beneficial bacteria.
3. Hang-on-back (HOB): All-in-one solution for small tanks; low flow, easy to maintain.
4. Canister filters: Roomy, customisable, robust—suiting most tank types.
5. Sump systems: High flow setups perfect for large or high-waste tanks like goldfish or predator systems.

Flow Rate Tip: For low-stock tanks, target 4× water turnover. For heavy stocking, aim for 6–10× turnover. E.g., 20 L tank → filter rated 80–200 L/h.

🌡️ 4. Temperature & Aeration

Most aquarium fish prefer 24–27 °C (tropical range). Use a reliable heater with built-in thermostat and independent thermometer.

Cold-water fish like danios or goldfish may not need heaters. Axolotls may even require a chiller below tropical care.

Oxygen: Add aeration via air pumps for extra oxygen. Live plants also oxygenate while removing waste—potentially eliminating the need for an air stone.

💡 5. Lighting—More Than a Pretty Display

Lighting impacts plant growth and fish health. Choose based on:

• Brightness: Low for basic viewing; high (e.g. 50–100 μmol photons) for plant growth.
• Spread: Wider tanks need broader light coverage; deeper tanks may need stronger output.
• Features: Many LED lights offer timers, color control via Bluetooth/Wi‑Fi.

Budget varies widely—$50 for simple LEDs, up to $1,500 for premium, feature-rich fixtures.

🪨 6. Substrate Choices

Substrate supports fish behavior, plant roots, and aesthetic goals:

• Inert gravel/sand: Doesn’t affect water chemistry—good for general use.
• Coral sand: Raises pH & hardness—best for African cichlids.
• Plant soil (pelletized): Nutrient-rich—ideal for planted tanks, but muddying dust may occur.
• Shrimp soil: Low-nutrient, soft, slightly acidic—perfect for shrimp setups.
• Decorative colored gravel: Rarely recommended unless aesthetic priority outweighs function.

🔬 7. Water Chemistry—Keep It Stable

Fish thrive on consistency. Key parameters to know:

• pH: 7 = neutral. <7 = acidic. >7 = alkaline.
• KH: Carbonate hardness—buffers pH resistant to sudden shifts.
• GH: General hardness—minerals like Ca²⁺/Mg²⁺; affects tissue health.

Tape water tends to be 7.5–7.8 in many regions. Regular 20% water changes help maintain stability. Adjust chemistry gently via substrate choices—plants, driftwood, gravel—rather than chemical dosing, which can cause parameter “rollercoasters.”

⚙️ 8. Installation Step‑by‑Step

1. Place tank away from direct sunlight to prevent algae blooms and heating.
2. Ensure stand is level and sturdy.
3. Add cushioning: Foam or mat under glass.
4. Set substrate and hardscape (rocks/wood).
5. Fill with dechlorinated water.
6. Install equipment: filter, heater, light, aerator.
7. Condition the water: Use additive to neutralise chlorine/chloramine.
8. Add beneficial bacteria: Kickstart the nitrogen cycle (2–3 weeks typical).
9. Test ammonia/nitrite: Wait until zero before adding fish slowly.
10. Slow introduction: Add a few fish at a time, feed sparingly for first 3 months to allow bio-filtration stabilisation.

🛠️ 9. Maintenance Routine

• Daily: Feed fish, observe behaviour, note irregularities.
• Weekly: 20% water change to reduce nitrate and replenish minerals.
• Monthly: Clean filter sponges, replace carbon/resins.
• Quarterly: Inspect and clean impeller, tubing, heater, lights.

❓ 10. Frequently Asked Questions

How many fish can I keep?

Use stocking formulas (e.g., 1 cm fish per 1 L of water), but remember filtration, behaviour, and territorial needs—better to under‑stock and add later.

How much should I feed?

Feed an amount fish can consume in 2–3 minutes, once or twice daily. Overfeeding pollutes water and stresses fish—just offer a bit more when new arrivals settle in.

What should I test for?

• Ammonia & nitrite: Should be 0 ppm after cycling.
• Nitrate: Keep under 40 ppm, or reduce via water changes/plants.
• pH, KH, GH: Less critical for varied-stock tanks—more important for sensitive species.

🐾 11. Pet Health & Veterinary Perspective

Beyond equipment, fish health matters. Watch for:

• Changes in behaviour: Lethargy, hiding, or flashing on decorations may signal stress or disease.
• Physical signs: White spots, bloating, torn fins, dead patches—all require action.
• Quarantine: Always quarantine new fish for 2 weeks to prevent introducing disease.
• Ask A Vet support: Use our app to chat with a professional vet for diagnosis, treatment suggestions, and care plans tailored to your fish.

🔧 12. Common Beginner Mistakes & Solutions

• Rushing stock additions: Endangers fish. Pro tip: add 1–3 fish, wait 2 weeks, retest before adding more.
• Overfeeding: Causes spikes in ammonia/nitrate. Stick to measured feeding times.
• Neglecting equipment: Impellers clog, lights dim—inspect regularly.
• Mixing incompatible species: Research compatibility; ask in‑store or via Ask A Vet for guidance.
• Ignoring cycling: Cycling prevents lethal ammonia/nitrite peaks; always wait until levels fall fully.

✅ Final Checklist Before You Begin

1. 𝐓ank size selected (give yourself growth room).
2. Filter chosen with mechanical, biological, (chemical) stages.
3. Heater/thermometer set at 24–27 °C.
4. Lighting matched to plants/fish needs.
5. Substrate chosen to support ecosystem goals.
6. Nitrogen cycle started—ammonia/nitrite at zero.
7. Maintenance plan in place: daily, weekly, monthly tasks.
8. Ask A Vet app downloaded for ongoing expert support 🩺.

🌟 In Summary

Setting up your first freshwater aquarium doesn’t have to be overwhelming. With the right equipment, a strong understanding of filtration, chemistry, and maintenance, and accessible vet support from Ask A Vet, you’ll build a thriving, joyful aquatic world.

Wishing you success on your aquarist journey! 🐠✨

If you ever need tailored advice or notice unusual signs in your fish, download the Ask A Vet app for professional support anytime.

– Dr Duncan Houston BVSc